If there are events queued and there is an exception in the main loop
of the UI code, it will print tracebacks on the console indefinitely.
Avoid that by improving the loop exit conditions.
(Bitbake rev: 2d0940b920a22b244f3ba6849c7cd019578386b4)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>