qt: Ignore showNormalIfMinimized in initialization or shutdown

Also get rid of ui_interface flag NOSHOWGUI. It's up to the GUI to
decide this.

Fixes #4360.

src/init.cpp

@@ -179,13 +179,13 @@ void HandleSIGHUP(int)
 
 bool static InitError(const std::string &str)
 {
-    uiInterface.ThreadSafeMessageBox(str, "", CClientUIInterface::MSG_ERROR | CClientUIInterface::NOSHOWGUI);
+    uiInterface.ThreadSafeMessageBox(str, "", CClientUIInterface::MSG_ERROR);
     return false;
 }
 
 bool static InitWarning(const std::string &str)
 {
-    uiInterface.ThreadSafeMessageBox(str, "", CClientUIInterface::MSG_WARNING | CClientUIInterface::NOSHOWGUI);
+    uiInterface.ThreadSafeMessageBox(str, "", CClientUIInterface::MSG_WARNING);
     return true;
 }
 

src/qt/bitcoingui.cpp

@@ -780,10 +780,6 @@ void BitcoinGUI::message(const QString &title, const QString &message, unsigned
         if (!(buttons = (QMessageBox::StandardButton)(style & CClientUIInterface::BTN_MASK)))
             buttons = QMessageBox::Ok;
 
-        // Ensure we get users attention, but only if main window is visible
-        // as we don't want to pop up the main window for messages that happen before
-        // initialization is finished.
-        if(!(style & CClientUIInterface::NOSHOWGUI))
         showNormalIfMinimized();
         QMessageBox mBox((QMessageBox::Icon)nMBoxIcon, strTitle, message, buttons, this);
         int r = mBox.exec();
@@ -921,6 +917,8 @@ void BitcoinGUI::setEncryptionStatus(int status)
 
 void BitcoinGUI::showNormalIfMinimized(bool fToggleHidden)
 {
+    if(!clientModel)
+        return;
     // activateWindow() (sometimes) helps with keyboard focus on Windows
     if (isHidden())
     {

src/ui_interface.h

@@ -63,8 +63,6 @@ public:
 
         /** Force blocking, modal message box dialog (not just OS notification) */
         MODAL               = 0x10000000U,
-        /** Don't bring GUI to foreground. Use for messages during initialization */
-        NOSHOWGUI           = 0x20000000U,
 
         /** Predefined combinations for certain default usage cases */
         MSG_INFORMATION = ICON_INFORMATION,