[Qt] make most Windows appear centered on main GUI

- remove default value for parent variable in dialogs, which should appear
  centered over main GUI and pass appropriate value
- add some addition NULL pointer checks

src/qt/aboutdialog.h

@@ -19,7 +19,7 @@ class AboutDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit AboutDialog(QWidget *parent = 0);
+    explicit AboutDialog(QWidget *parent);
     ~AboutDialog();
 
     void setModel(ClientModel *model);

src/qt/addressbookpage.cpp

@@ -158,6 +158,9 @@ void AddressBookPage::onCopyLabelAction()
 
 void AddressBookPage::onEditAction()
 {
+    if(!model)
+        return;
+
     if(!ui->tableView->selectionModel())
         return;
     QModelIndexList indexes = ui->tableView->selectionModel()->selectedRows();
@@ -167,7 +170,7 @@ void AddressBookPage::onEditAction()
     EditAddressDialog dlg(
         tab == SendingTab ?
         EditAddressDialog::EditSendingAddress :
-            EditAddressDialog::EditReceivingAddress);
+        EditAddressDialog::EditReceivingAddress, this);
     dlg.setModel(model);
     QModelIndex origIndex = proxyModel->mapToSource(indexes.at(0));
     dlg.loadRow(origIndex.row());

src/qt/addressbookpage.h

@@ -39,7 +39,7 @@ public:
         ForEditing  /**< Open address book for editing */
     };
 
-    explicit AddressBookPage(Mode mode, Tabs tab, QWidget *parent = 0);
+    explicit AddressBookPage(Mode mode, Tabs tab, QWidget *parent);
     ~AddressBookPage();
 
     void setModel(AddressTableModel *model);

src/qt/askpassphrasedialog.h

@@ -27,7 +27,7 @@ public:
         Decrypt     /**< Ask passphrase and decrypt wallet */
     };
 
-    explicit AskPassphraseDialog(Mode mode, QWidget *parent = 0);
+    explicit AskPassphraseDialog(Mode mode, QWidget *parent);
     ~AskPassphraseDialog();
 
     void accept();

src/qt/bitcoingui.cpp

@@ -10,12 +10,12 @@
 #include "guiconstants.h"
 #include "guiutil.h"
 #include "notificator.h"
+#include "openuridialog.h"
 #include "optionsdialog.h"
 #include "optionsmodel.h"
 #include "rpcconsole.h"
 #include "walletframe.h"
 #include "walletmodel.h"
-#include "openuridialog.h"
 
 #ifdef Q_OS_MAC
 #include "macdockiconhandler.h"
@@ -345,7 +345,7 @@ void BitcoinGUI::setClientModel(ClientModel *clientModel)
         setNumBlocks(clientModel->getNumBlocks(), clientModel->getNumBlocksOfPeers());
         connect(clientModel, SIGNAL(numBlocksChanged(int,int)), this, SLOT(setNumBlocks(int,int)));
 
-        // Receive and report messages from network/worker thread
+        // Receive and report messages from client model
         connect(clientModel, SIGNAL(message(QString,QString,unsigned int)), this, SLOT(message(QString,QString,unsigned int)));
 
         rpcConsole->setClientModel(clientModel);
@@ -460,21 +460,25 @@ void BitcoinGUI::optionsClicked()
 {
     if(!clientModel || !clientModel->getOptionsModel())
         return;
-    OptionsDialog dlg;
+
+    OptionsDialog dlg(this);
     dlg.setModel(clientModel->getOptionsModel());
     dlg.exec();
 }
 
 void BitcoinGUI::aboutClicked()
 {
-    AboutDialog dlg;
+    if(!clientModel)
+        return;
+
+    AboutDialog dlg(this);
     dlg.setModel(clientModel);
     dlg.exec();
 }
 
 void BitcoinGUI::openClicked()
 {
-    OpenURIDialog dlg;
+    OpenURIDialog dlg(this);
     if(dlg.exec())
     {
         emit receivedURI(dlg.getURI());

src/qt/editaddressdialog.h

@@ -31,7 +31,7 @@ public:
         EditSendingAddress
     };
 
-    explicit EditAddressDialog(Mode mode, QWidget *parent = 0);
+    explicit EditAddressDialog(Mode mode, QWidget *parent);
     ~EditAddressDialog();
 
     void setModel(AddressTableModel *model);

src/qt/openuridialog.h

@@ -16,7 +16,7 @@ class OpenURIDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit OpenURIDialog(QWidget *parent = 0);
+    explicit OpenURIDialog(QWidget *parent);
     ~OpenURIDialog();
 
     QString getURI();

src/qt/optionsdialog.h

@@ -21,7 +21,7 @@ class OptionsDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit OptionsDialog(QWidget *parent = 0);
+    explicit OptionsDialog(QWidget *parent);
     ~OptionsDialog();
 
     void setModel(OptionsModel *model);

src/qt/rpcconsole.h

@@ -19,7 +19,7 @@ class RPCConsole: public QDialog
     Q_OBJECT
 
 public:
-    explicit RPCConsole(QWidget *parent = 0);
+    explicit RPCConsole(QWidget *parent);
     ~RPCConsole();
 
     void setClientModel(ClientModel *model);

src/qt/signverifymessagedialog.h

@@ -18,7 +18,7 @@ class SignVerifyMessageDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit SignVerifyMessageDialog(QWidget *parent = 0);
+    explicit SignVerifyMessageDialog(QWidget *parent);
     ~SignVerifyMessageDialog();
 
     void setModel(WalletModel *model);

src/qt/transactionview.cpp

@@ -83,14 +83,12 @@ TransactionView::TransactionView(QWidget *parent) :
 
     addressWidget = new QLineEdit(this);
 #if QT_VERSION >= 0x040700
-    /* Do not move this to the XML file, Qt before 4.7 will choke on it */
     addressWidget->setPlaceholderText(tr("Enter address or label to search"));
 #endif
     hlayout->addWidget(addressWidget);
 
     amountWidget = new QLineEdit(this);
 #if QT_VERSION >= 0x040700
-    /* Do not move this to the XML file, Qt before 4.7 will choke on it */
     amountWidget->setPlaceholderText(tr("Min amount"));
 #endif
 #ifdef Q_OS_MAC
@@ -355,10 +353,10 @@ void TransactionView::editLabel()
             // Determine type of address, launch appropriate editor dialog type
             QString type = modelIdx.data(AddressTableModel::TypeRole).toString();
 
-            EditAddressDialog dlg(type==AddressTableModel::Receive
+            EditAddressDialog dlg(
+                type == AddressTableModel::Receive
                 ? EditAddressDialog::EditReceivingAddress
-                                         : EditAddressDialog::EditSendingAddress,
-                                  this);
+                : EditAddressDialog::EditSendingAddress, this);
             dlg.setModel(addressBook);
             dlg.loadRow(idx);
             dlg.exec();