Empty tooltips shown by debugger

1. Enable "Use tooltips in main editor while debugging".
2. Create a new Qt GUI project.
3. Build it.
4. Set a breakpoint in main.cpp.
5. Run it in debugger.
6. When execution stopped at the breakpoint, hover the class names MainWindow or QApplication.
   An empty tooltip will show up.

The tooltip should present useful information to the user. If there is nothing to show, no tooltip should be shown at all.