fix: Avoid unlocking too early and fix collaboration in Word

[juliusknorr]

Fix #419

Summary

It seems that OOS sends UNLOCK requests instead of GET_LOCK with GetCurrentLock-00000000-0000-0000-0000-000000000000 as a lock token just to check the current lock. Also we still need the officeonline table for storing and comparing the lock tokens, as the server locking API currently doesn't expose methods to store a custom token.

Known issues to be documented in the README:

• UNLOCK might not happen if the browser terminates the request (Chrome)
  • https://stackoverflow.com/questions/62062629/office-online-server-didnt-send-unlock-action-when-i-closed-the-session
  • https://social.msdn.microsoft.com/Forums/office/en-US/1b783d1c-c686-4b2d-b23f-4977e6bed806/wopi-unlock-call-never-gets-triggered-in-chrome-and-latest-edge-browser?forum=os_office

[luka-nextcloud]

@juliushaertl Seems like the switch-case statements are missing default case handlers.

[juliusknorr]

@luka-nextcloud Expected in this case as we don't have a default path and just continue with the execution path.