QmlObserver: Prevent messages from being sent if there is no server side

Actually this is fixed in QDeclarativeService::sendMessage, too, but the
fix won't be part of 4.7.1, so better double-check.

Reviewed-by: Christiaan Janssen

share/qtcreator/qml/qmljsdebugger/include/qdeclarativeobserverservice.h

@@ -70,6 +70,8 @@ public:
     void reloaded();
     QString idStringForObject(QObject *obj) const;
 
+    void sendMessage(const QByteArray &message);
+
 public Q_SLOTS:
     void selectedColorChanged(const QColor &color);
     void contextPathUpdated(const QStringList &contextPath);