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/qmljsinspector.cpp

@@ -261,6 +261,11 @@ void InspectorUi::debugQueryUpdated(QDeclarativeDebugQuery::State newState)
     disconnect(m_debugQuery,SIGNAL(stateChanged(QDeclarativeDebugQuery::State)),this,SLOT(debugQueryUpdated(QDeclarativeDebugQuery::State)));
 }
 
+bool InspectorUi::isConnected() const
+{
+    return m_clientProxy;
+}
+
 void InspectorUi::connected(ClientProxy *clientProxy)
 {
     m_clientProxy = clientProxy;