debugger: Do not display empty tooltips

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

src/plugins/debugger/gdb/gdbengine.cpp

@@ -3734,10 +3734,9 @@ bool GdbEngine::showToolTip()
         return true;
     }
 
-    const QModelIndex index = watchHandler()->itemIndex(iname);
-    if (!index.isValid()) {
+    if (!watchHandler()->isValidToolTip(iname)) {
         watchHandler()->removeData(iname);
-        return false;
+        return true;
     }
     DebuggerToolTipWidget *tw = new DebuggerToolTipWidget;
     tw->setExpression(expression);