Handle "Mailbox already exists" on folder creation

[glennmorris]

Using offlineimap 8.0.0 on Fedora 36, I've just encountered the issue where offlineimap fails creating a new (nested) folder.
This is with office365, where the error message from the server is (when trying to create "work/subfolder"):

ERROR: Folder 'work'[RemoteServer] could not be created. Server responded: ('NO', [b'Mailbox already exists.'])

This was previously reported as an offlineimap issue, which is listed in your issue 18 as an item to be solved.

The patch from offlineimap pull request 646 fixes it for me. It was applied to offlineimap's next branch, but not to master.

Please consider applying this patch or some version of it.

Thanks!

[stefmorp]

I confirm, issue still exists on 8.0.0 - workaround is to create the nested subfolder manually on both sides. Applying the patch would be appreciated!