Show input box to filter torrent list only when the list is shown

It's misleading to show the filter on every tab when it works only
for the torrent list.

src/mainwindow.cpp

@@ -181,6 +181,14 @@ MainWindow::MainWindow(QWidget *parent, const QStringList& torrentCmdLine) : QMa
   hSplitter->setChildrenCollapsible(false);
   hSplitter->setContentsMargins(0, 4, 0, 0);
 
+  // Name filter
+  search_filter = new LineEdit();
+  searchFilterAct = toolBar->insertWidget(actionLock_qBittorrent, search_filter);
+  search_filter->setFixedWidth(200);
+  QWidget *spacer = new QWidget(this);
+  spacer->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
+  toolBar->insertWidget(searchFilterAct, spacer);
+
   // Transfer List tab
   transferList = new TransferListWidget(hSplitter, this, QBtSession::instance());
   properties = new PropertiesWidget(hSplitter, this, transferList);
@@ -193,15 +201,9 @@ MainWindow::MainWindow(QWidget *parent, const QStringList& torrentCmdLine) : QMa
   vSplitter->setCollapsible(1, false);
   tabs->addTab(vSplitter, IconProvider::instance()->getIcon("folder-remote"), tr("Transfers"));
 
-  vboxLayout->addWidget(tabs);
-  // Name filter
-  search_filter = new LineEdit();
   connect(search_filter, SIGNAL(textChanged(QString)), transferList, SLOT(applyNameFilter(QString)));
-  QAction *searchFilterAct = toolBar->insertWidget(actionLock_qBittorrent, search_filter);
-  search_filter->setFixedWidth(200);
-  QWidget *spacer = new QWidget(this);
-  spacer->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
-  toolBar->insertWidget(searchFilterAct, spacer);
+
+  vboxLayout->addWidget(tabs);
 
 
   prioSeparator = toolBar->insertSeparator(actionDecreasePriority);
@@ -495,8 +497,11 @@ void MainWindow::tab_changed(int new_tab) {
   if (tabs->currentWidget() == vSplitter) {
     qDebug("Changed tab to transfer list, refreshing the list");
     properties->loadDynamicData();
+    searchFilterAct->setVisible(true);
     return;
   }
+  else
+    searchFilterAct->setVisible(false);
   if (tabs->currentWidget() == searchEngine) {
     qDebug("Changed tab to search engine, giving focus to search input");
     searchEngine->giveFocusToSearchInput();

src/mainwindow.h

@@ -184,6 +184,7 @@ private:
   bool force_exit;
   bool ui_locked;
   LineEdit *search_filter;
+  QAction *searchFilterAct;
   // Keyboard shortcuts
   QShortcut *switchSearchShortcut;
   QShortcut *switchSearchShortcut2;