debugger: Do not display empty tooltips

Task-number: QTCREATORBUG-6893
Change-Id: Idb780e97c23f6cc5d1bcede149959b2e58f9eaa2
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/debugger/watchhandler.h

@@ -203,6 +203,7 @@ public:
 
     void scheduleResetLocation();
     void resetLocation();
+    bool isValidToolTip(const QByteArray &iname) const;
 
 private:
     friend class WatchModel;