Bug 34963: Restore the ability to blank fields when editing a suggestion

Bug 34963: Restore the ability to blank fields when editing a suggestion

Regression introduced by bug 23991.
We don't want to remove the fields from the edition if they are empty.

Ideally we should have separate parameters for edition and search, but
this is the low-effort fix, and hopefully won't introduce side-effects.

Test plan:
Try to edit a suggestion and blank some fields
Try to search for suggestions using the search form on the left of the
screen

Signed-off-by: Ray Delahunty <lib-systems@arts.ac.uk>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit cd1f4145fe091314895a4f8a4f73a5b3a5f8bb87)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>