QuickDesigner: Fix crash on exit

Make sure that the sidebar items are deleted before the core
(e.g. ICore::instance()) is deleted.

Task-number: QTCREATORBUG-3269
Reviewed-by: Thomas Hartmann

src/plugins/qmldesigner/designmodewidget.cpp

@@ -670,6 +670,9 @@ void DesignModeWidget::setup()
     connect(m_leftSideBar, SIGNAL(availableItemsChanged()), SLOT(updateAvailableSidebarItemsRight()));
     connect(m_rightSideBar, SIGNAL(availableItemsChanged()), SLOT(updateAvailableSidebarItemsLeft()));
 
+    connect(Core::ICore::instance(), SIGNAL(coreAboutToClose()),
+            this, SLOT(deleteSidebarWidgets()));
+
     m_fakeToolBar->setToolbarCreationFlags(Core::EditorToolBar::FlagsStandalone);
     //m_fakeToolBar->addEditor(textEditor()); ### what does this mean?
     m_fakeToolBar->setNavigationVisible(false);
@@ -738,6 +741,14 @@ void DesignModeWidget::updateAvailableSidebarItemsLeft()
     m_leftSideBar->setUnavailableItemIds(m_rightSideBar->unavailableItemIds());
 }
 
+void DesignModeWidget::deleteSidebarWidgets()
+{
+    delete m_leftSideBar;
+    delete m_rightSideBar;
+    m_leftSideBar = 0;
+    m_rightSideBar = 0;
+}
+
 void DesignModeWidget::resizeEvent(QResizeEvent *event)
 {
     if (m_warningWidget)

src/plugins/qmldesigner/designmodewidget.h

@@ -148,6 +148,8 @@ private slots:
     void updateAvailableSidebarItemsLeft();
     void updateAvailableSidebarItemsRight();
 
+    void deleteSidebarWidgets();
+
 protected:
     void resizeEvent(QResizeEvent *event);