Bug 11572: ensure that running Z39.50 search from staff search results detects ISBN

Bug 11572: ensure that running Z39.50 search from staff search results detects ISBN

In Koha 3.8, if a standard catalog search was performed and the user
clicked the Z39.50 search button, the search string would automatically
be placed in the isbn field for the Z39.50 search form.
Changes to the code have since broken this functionality.

Test Plan:
1) From mainpage.pl, use "Search the catalog" to search for the string
   "9781570672835"
2) Click the Z39.50 Search button
3) Note the string is placed in the title field
4) Apply this patch
5) Repeat steps 1-2
6) Note the string is placed in the isbn field

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Tested old and new ISBN with and without hyphens.
Also tested some other keyword searches.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Note that the behavior will be a bit odd if you do a 'replace via
Z39.50' from a bib record whose title happens to be an ISBN, but
this scenario seems unlikely enough to ignore.