Bug 14553: Silencing warn triggered when clearing item rating on OPAC

Bug 14553: Silencing warn triggered when clearing item rating on OPAC

To test:

1) Go to any item and clear the star rating (don't have to set a rating first)
2) Notice the warn
3) Apply patch and reload page
4) Clear star rating
5) Notice no warn
6) Click a star to add a rating
7) Make sure your rating, the average rating and amount of votes are all
   correct
8) Could be beneficial to log in as another user and try to add a rating on the
   same item from their account. Check the average rating is
   cacalculated and amount of votes increases
9) Confirm still no warns

Signed-off-by: Frederic Demians <f.demians@tamil.fr>
  Can see the warning in logs, and its disappearance with this patch.
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>