Fix #4502: Rare crash during shutdown when switching GroupDialog tabs

Don't use wxWindow::RemoveChild(), instead just call the delete operator
on the window to be destroyed; it will automatically remove itself from
its parent.

radiant/ui/mainframe/EmbeddedLayout.cpp

@@ -118,7 +118,7 @@ void EmbeddedLayout::deactivate()
     GlobalXYWndManager().destroyViews();
 
     // Delete the CamWnd
-    _camWnd = CamWndPtr();
+    _camWnd.reset();
 
     // Give the notebook back to the GroupDialog
     GlobalGroupDialog().reparentNotebookToSelf();
@@ -132,13 +132,11 @@ void EmbeddedLayout::deactivate()
     _posHPane.disconnect();
     _posGroupCamPane.disconnect();
 
-    wxFrame* topLevelParent = GlobalMainFrame().getWxTopLevelWindow();
-    topLevelParent->RemoveChild(_horizPane);
-    _horizPane->Destroy();
+	delete _horizPane;
 
     // Those two have been deleted by the above, so NULL the references
-    _horizPane = NULL;
-    _groupCamPane = NULL;
+    _horizPane = nullptr;
+    _groupCamPane = nullptr;
 }
 
 void EmbeddedLayout::maximiseCameraSize()

radiant/ui/mainframe/RegularLayout.cpp

@@ -121,17 +121,15 @@ void RegularLayout::deactivate()
 	GlobalXYWndManager().destroyViews();
 
 	// Delete the CamWnd
-	_camWnd = CamWndPtr();
+	_camWnd.reset();
 
 	// Hide the group dialog
 	GlobalGroupDialog().hideDialogWindow();
 
-	wxFrame* topLevelParent = GlobalMainFrame().getWxTopLevelWindow();
-	topLevelParent->RemoveChild(_regular.horizPane);
-	_regular.horizPane->Destroy();
+	delete _regular.horizPane;
 
-	_regular.horizPane = NULL;
-	_regular.texCamPane = NULL;
+	_regular.horizPane = nullptr;
+	_regular.texCamPane = nullptr;
 }
 
 void RegularLayout::maximiseCameraSize()

radiant/ui/mainframe/SplitPaneLayout.cpp

@@ -205,7 +205,7 @@ void SplitPaneLayout::deconstructLayout()
 	GlobalXYWndManager().destroyViews();
 
 	// Delete the CamWnd
-	_camWnd = CamWndPtr();
+	_camWnd.reset();
 
 	// Hide the group dialog
 	GlobalGroupDialog().hideDialogWindow();
@@ -214,9 +214,7 @@ void SplitPaneLayout::deconstructLayout()
 	GlobalGroupDialog().removePage("textures");
 
 	// Destroy the widgets, so it gets removed from the main container
-	wxFrame* topLevelParent = GlobalMainFrame().getWxTopLevelWindow();
-	topLevelParent->RemoveChild(_splitPane.horizPane);
-	_splitPane.horizPane->Destroy();
+	delete _splitPane.horizPane;
 
 	_splitPane.clear();
 }