Removal option appears on favorites of other user if the favorited sentence doesn't exist

[Yorwba]

To Reproduce

1. Go to the profile of another user who has favorited a sentence that has been deleted.
2. Click the cross next to the sentence, seemingly indicating that it can be removed.
3. A message indicates that the favorite has been removed successfully.
4. Reload the page.
5. Note that the favorite hasn't actually been removed.

Expected behavior
The option to remove the favorite shouldn't appear unless you're looking at your own favorites. Also, when removing a favorite fails for whatever reason, an error message should be displayed.

Screenshots

Additional information
Reported on the wall: https://tatoeba.org/en/wall/show_message/37404#!#message_37404