Fix bug in MainWindow::setActiveWindow

The method MainWindow::setActiveWindow() must not automatically add a view to the mdi area if it's not part of it because this causes a crash when trying to make a fullscreen window or undock a view.
Instead the calling instance must explicitly call MainWindow::addWindow where needed.

src/Gui/MainWindow.cpp

@@ -997,10 +997,8 @@ void MainWindow::onSetActiveSubWindow(QWidget *window)
 
 void MainWindow::setActiveWindow(MDIView* view)
 {
-    if(!view || d->activeView == view)
+    if (!view || d->activeView == view)
         return;
-    if(!windows().contains(view->parentWidget()))
-        addWindow(view);
     onSetActiveSubWindow(view->parentWidget());
     d->activeView = view;
     Application::Instance->viewActivated(view);