QmlProfiler: show empty trace

In the case that the application did not generate any event
after running the profiler, still show an empty trace.
Otherwise the user will think that the profiler didn't work.

Change-Id: Idd15225270d55d834719f66387864433fcb9026d
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/plugins/qmlprofiler/qml/MainView.qml

@@ -176,6 +176,7 @@ Rectangle {
 
     function clearAll() {
         clearDisplay();
+        elapsedTime = 0;
     }
 
     function nextEvent() {