Fix several compiler warnings

* -Wmaybe-uninitialized
* -Wunused-parameter
* -Wunused-variable
* -Wnonnull
* -Wstringop-truncation
* -Wstringop-overflow

src/Gui/OverlayManager.cpp

@@ -1178,7 +1178,7 @@ public:
         OverlayTabWidget *dst = nullptr;
         int dstIndex = -1;
         QDockWidget *dstDock = nullptr;
-        Qt::DockWidgetArea dstDockArea;
+        Qt::DockWidgetArea dstDockArea {};
 
         if (!tabWidget) {
             rect = QRect(pos - dragOffset, dragSize);