Bug 22778: Suggestions with no "suggester" can cause errors

Bug 22778: Suggestions with no "suggester" can cause errors

If one tries to modify a suggestion that has no suggester you will get the following error:

Can't call method "lang" on an undefined value at /usr/share/koha/lib/C4/Suggestions.pm line 506

Koha assumes that every suggestion has a borrowernumber in suggestedby

Test Plan:
1) Create a suggestion with an unpopulated suggestedby
2) Attempt to modify that suggestion
3) Note the error
4) Apply this patch
5) Restart all teh things
6) Attempt to modify that suggestion
7) No error!

Signed-off-by: David Roberts <david@koha-ptfs.co.uk>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>