Debugger: Fix exit crash in debug mode (X11).

Double deletion of debug mode widgets.

src/plugins/coreplugin/navigationwidget.cpp

@@ -79,8 +79,10 @@ NavigationWidgetPlaceHolder::NavigationWidgetPlaceHolder(Core::IMode *mode, QWid
 NavigationWidgetPlaceHolder::~NavigationWidgetPlaceHolder()
 {
     if (m_current == this) {
-        NavigationWidget::instance()->setParent(0);
-        NavigationWidget::instance()->hide();
+        if (NavigationWidget *nw = NavigationWidget::instance()) {
+            nw->setParent(0);
+            nw->hide();
+        }
     }
 }
 

src/plugins/debugger/debuggermainwindow.cpp

@@ -507,6 +507,7 @@ QWidget *DebuggerMainWindow::createContents(IMode *mode)
     splitter->addWidget(mainWindowSplitter);
     splitter->setStretchFactor(0, 0);
     splitter->setStretchFactor(1, 1);
+    splitter->setObjectName(QLatin1String("DebugModeWidget"));
     return splitter;
 }
 

src/plugins/debugger/debuggerplugin.cpp

@@ -1117,8 +1117,7 @@ DebuggerPluginPrivate::~DebuggerPluginPrivate()
     delete m_debuggerSettings;
     m_debuggerSettings = 0;
 
-    delete m_mainWindow;
-    m_mainWindow = 0;
+    // Mainwindow will be deleted by debug mode.
 
     delete m_snapshotHandler;
     m_snapshotHandler = 0;