debugger: fix some (non-)leak

Task-number: QTCREATORBUG-2334

src/plugins/debugger/debuggerplugin.cpp

@@ -2539,6 +2539,9 @@ DebuggerPlugin::~DebuggerPlugin()
     delete d->m_uiSwitcher;
     d->m_uiSwitcher = 0;
 
+    delete d->m_commandWindow;
+    d->m_commandWindow = 0;
+
     delete d;
 }