Bug 26364: Don't discard the passed isbn

Bug 26364: Don't discard the passed isbn

I don't know, if we get rid fo this check we can now check the db for the same isbn we passed

This may be useful as we may want to see the biblio with the same isbn as long as number is different?

This will make tests fail

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit feb7f5f6dd89f58f3b027898705fb0fa57a051ab)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>