PICARD-2991: Handle statvfs errors on file rename

[phw]

Summary

• This is a…
  • Bug fix
  • Feature addition
  • Refactoring
  • Minor / simple change (like a typo)
  • Other
• Describe this change in 1-2 sentences:

Problem

• JIRA ticket (optional): PICARD-2991

make_short_filename runs _get_filename_limit on the basedir, which in turn tries to get filename limits by calling statvfs. statvfs can fail with FileNotFoundError or PermissionError.

To reproduce:

• In Options > File naming set the target dir to something on which os.statvfs fails. On my Linux system this is e.g. /run/user/1000/doc
• Save options and reopen the options dialog

=> File naming failed to load, exception is logged

Solution

1. If in _get_filename_limit the call to os.statvfs fails, retry on the parent path
2. Do not fail to load the options dialog on FileNotFoundError or PermissionError when updating the examples

[zas]

LGTM