Bug 37366: Patron category "Password change in OPAC" setting only follows system...

Bug 37366: Patron category "Password change in OPAC" setting only follows system preference

In Administration > Patron categories, when setting the Password change in OPAC field, Koha will not save "Allowed" or "Not allowed" options, and will only keep "Follow the system preference OPACPasswordChange..." value.

Test Plan:
1) Change the Password change in OPAC field
2) Note the change doesn't take affect
3) Apply this patch
4) Change the field again
5) This time is stays!

Signed-off-by: Roman Dolny <roman.dolny@jezuici.pl>
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>