FIX: Safer close

[larsoner]

Qt callbacks should never raise an error or you get a segfault:

https://github.com/mne-tools/mne-python/pull/9803/checks?check_run_id=3796599057

E   subprocess.CalledProcessError: Command '['/opt/hostedtoolcache/Python/3.9.7/x64/bin/python', '-uc', "import mne; mne.viz.create_3d_figure((800, 600)); backend = mne.viz.get_3d_backend(); assert backend == 'pyvistaqt', backend"]' died with <Signals.SIGABRT: 6>.
...
Traceback (most recent call last):

  File "/opt/hostedtoolcache/Python/3.9.7/x64/lib/python3.9/site-packages/pyvistaqt/plotting.py", line 602, in close

    self.app_window.close()

RuntimeError: wrapped C/C++ object of type MainWindow has been deleted

This PR just more safely wraps the handler in a try/except to avoid this.

[akaszynski]

LGTM. Thanks!

GitHub actions appears to be degraded at the moment...

[larsoner]

@akaszynski thanks for the quick review. @GuillaumeFavelier can you look and merge if you're happy?

[GuillaumeFavelier]

LGTM, thanks for the addition @larsoner