fwhosts.cgi: Fixes bug#13206 - no validation of location group name

fwhosts.cgi: Fixes bug#13206 - no validation of location group name

- Added validation code for the location group name. This is only validated when edited
   and not when created.
- The code was copied from the section for creating the Services Group Name or the
   Network/Host Group Name.

Fixes: Bug#13206
Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Stefan Schantl <stefan.schantl@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>