Unlocking a page raises exception #367

In djangocms_versioning/admin.py:1276 (unlock_view) the function notify_version_author_version_unlocked is called which itself attempts to send an email to the user owning the lock.

However, if the project configuration does not configure an email backend, then this function can't connect and raises

OSError: [Errno 101] Network is unreachable.

In my opinion, such a network issue shall be logged but not cause an internal server error.