Fix crash after unloading project and changing qt versions

Unloading a project must always remove the configuration widgets, since
otherwise they might be accessed after the project was deleted. So
remove them even if we have no other project widget to show.

Reviewed-By: Tobias Hunger

src/plugins/projectexplorer/projectwindow.cpp

@@ -365,8 +365,10 @@ void ProjectWindow::startupProjectChanged(ProjectExplorer::Project *p)
 
 void ProjectWindow::showProperties(int index, int subIndex)
 {
-    if (index < 0 || index >= m_tabIndexToProject.count())
+    if (index < 0 || index >= m_tabIndexToProject.count()) {
+        removeCurrentWidget();
         return;
+    }
 
     Project *project = m_tabIndexToProject.at(index);