fix(encryption): Fix mountpoint check to accept if several are found

[come-nc]

Summary

There is no strong requirement to have only one mount for a given
storage id. Also the error in this case would be misleading.

Avoids errors "Could not find mount point, can't keep encryption keys" in situations where several mounts are found for the storage.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[come-nc]

/backport to stable29

[come-nc]

/backport to stable28

[danxuliu]

This introduced a regression when using groupfolders and encryption. Now it is no longer possible to move a file from a groupfolder to the home storage if the encryption module is enabled, even if neither the groupfolder nor the home storage are encrypted (this is unrelated to nextcloud/groupfolders#2942, which fixes moving files into an encrypted groupfolder).

This is reproducible in latest master and stable30, but also on stable29 and stable28 due to the backports; it is already present in Nextcloud 28.0.9rc1 and 29.0.5rc1.

How to reproduce

• Enable the default encryption module (occ app:enable encryption)
• Enable encryption (occ config:app:set --value=yes core encryption_enabled)
• Optionally (it does not matter if encryption is enabled or not for the home storage, but maybe it can help debugging the issue), disable encryption in the home storage (occ config:app:set --value=0 encryption encryptHomeStorage)
• Enable groupfolders (occ app:enable groupfolders)
• Create a groupfolder (occ groupfolders:create test_group_folder)
• Add group to groupfolder (occ groupfolders:group 1 admin read write share delete)
• Upload file into the groupfolder (curl --user admin:admin --upload-file /PATH/TO/test.txt --header "OCS-APIRequest: true" http://127.0.0.1:8000/remote.php/dav/files/admin/test_group_folder/test.txt)
• Try to move file from groupfolder to home (curl --user admin:admin --request MOVE --header "OCS-APIRequest: true" --header "Destination: http://127.0.0.1:8000/remote.php/dav/files/admin/test.txt" "http://127.0.0.1:8000/remote.php/dav/files/admin/test_group_folder/test.txt")

Expected result

The file is moved

Actual result

An internal error occurs:

  <s:exception>BadMethodCallException</s:exception>
  <s:message>path needs to be relative to the system wide data folder and point to a user specific file</s:message>