Qml debugging causes app to hang if qml debugger fails to connect within first few secs

If Qml debugger fails to connect within the first few seconds it causes the debugged app to hang indefinitely.

Steps to reproduce the issue:

1. run the attached project
2. wait for 5-10sec before closing the message box
3. => app hangs

with a shorter delay in step 2 the problem would not occur.

Reattaching the debugger fixes the hanging.