Bug 8018: MARC framework max subfield length should default to 9999

Bug 8018: MARC framework max subfield length should default to 9999

The default value for the marc_subfield_structure.maxlenght is 9999
in the DB. Currently the template passes an empty value which is casted to
0 by the CGI.

This simple patch validates the input and converts to the default (9999)
if not defined or 0.

Another approach could be changing the 9999 default and/or treating 0 as
'no-limit'.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Works by defaulting 0 or "" to 9999.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 1ebbf40ecc07b9474e81e20ec1598659ab027d7a)
Signed-off-by: Fridolin SOMERS <fridolin.somers@biblibre.com>