Bug 26364: Remove false matches on isbn

Bug 26364: Remove false matches on isbn

The test here was returning 0590353403 when searched for 9780590353403
because of the regex matching

Koha doesn't work this way unless SearchWithISBNVariations is set to 'search'
and you use a dropdown to select ISBN for searching

To test:
1 - Search catalog for nb=9780590353403
2 - Confirm you don't have results, or delete the records with results
3 - Add isbn 0590353403 to a record
4 - Repeat search, fails
5 - Enable SearchWithISBNVariations
6 - Repeat search, fails
7 - Go to advanced search, select ISBN, search for 9780590353403
8 - Get results

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>