Bug 29696: Preserve link to biblio when creating a suggestion

Bug 29696: Preserve link to biblio when creating a suggestion

Caused by
  commit 586bed1319592e05f5dc3acf64a1dba8cae69d6b
  Bug 28941: Filter suggestion inputs at the OPAC

We are loosing the link with the biblio (suggestion.biblionumber)

Test plan:
At the OPAC, go to the detail page of a bibliographic record, click
"Suggest for purchase" and submit the form.
Without this patch the suggestion is created but the link to the
bibliographic record is lost
With this patch applied you should see that suggestions.biblionumber has
correctly been preserved

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>