Ignore errors in do_window_cleanup to fix shutdown issue

[abdnh]

Closes #3126

I was able to reproduce it by changing time_to_wait too (and having auto sync enabled).

[voczi]

Figured out you could just do it like this:
if self._x_timer and not sip.isdeleted(self._x_timer):
Repeat for every timer in that method.

Docs for the single_shot method did also mention this.

[abdnh]

Yes, I thought of that, but preferred to go for less code.

[dae]

Great, thanks Abdo!