Bug 18804: (bug 13501 follow-up) Fix add item form (select2)

Bug 18804: (bug 13501 follow-up) Fix add item form (select2)

Hard to say here, select2 adds so many elements that we need to ignore.
Here we just assume that input text with an id starting with
tag_952_subfield must be filled

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Lee Jamison <ldjamison@marywood.edu>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
(cherry picked from commit 8035a467f0b5d8441d4164bc183286d4f2593438)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>