[stable9] Properly handle deleted users in UserMountCache

[PVince81]

Backport of #27028 to stable9

[mention-bot]

@PVince81, thanks for your PR! By analyzing the history of the files in this pull request, we identified @icewind1991, @nickvergessen and @LukasReschke to be potential reviewers.

[PVince81]

Hmm, seems I can't reproduce the issue using #27012 (comment) on stable9. And the fix doesn't clean up the bogus entry.

Might as well close this. At least there is no visible exception or issue.

[PVince81]

hmm, not reproducible on stable9.1 either... needs further research

[PVince81]

Retested this, it works.

Steps here #27012 (comment) and require the activity app to be enabled.

Please note that the symptoms on stable9 are different than in the original issue.
In the original issue there is a clear error in the UI when commenting, but on stable9 the comment is posted and the error appears in the log only. Also, no activity is posted for the comment on stable9.
After this fix, no error in log and activity comment is posted properly.

Please review @jvillafanez @DeepDiver1975 @butonic (<= it was based on your patch)

[jvillafanez]

👍

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.