QmlJSInspector: Fix disconnect() warnings on users app shutdown

Don't try to disconnect from the proxy if you haven't been connected
before, e.g. because the QmlJSObserverService is missing.

Reviewed-by: Christiaan Janssen

src/plugins/qmljsinspector/qmljsinspectorplugin.cpp

@@ -140,7 +140,8 @@ void InspectorPlugin::objectAdded(QObject *object)
 void InspectorPlugin::aboutToRemoveObject(QObject *obj)
 {
     if (m_clientProxy && m_clientProxy->qmlAdapter() == obj) {
-        m_inspectorUi->disconnected();
+        if (m_inspectorUi->isConnected())
+            m_inspectorUi->disconnected();
         delete m_clientProxy;
         m_clientProxy = 0;
     }