Bug 19808: Handle deleted reviewers gracefully - opac-detail

Bug 19808: Handle deleted reviewers gracefully - opac-detail

And other display issues when the patron was NULL.
Which allows to keep the review even if it has no patron.
Because it might be useful.

For example when disconnected, the borrowernumber is null. So the
comments from deleted patrons were displayed as if the disconnected
user wrote them. So it had the edit button...

And fix borrowernumber not being passed to the template when
OpacStarRatings was false.

Test plan
1. Log in as a patron
2. Leave a comment/review on a record
3. Librarian: approve this comment
4. Delete the borrower
5. See the record (opac:/cgi-bin/koha/opac-detail.pl?biblionumber=RELEVANT_BIB_NUMBER)
6. Then you should see an error
7. Apply this patch
8. Refresh the page
9. Then you should see the record page with the comment

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jon Knight <J.P.Knight@lboro.ac.uk>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>