Bug 8714 - Poorly ordered and triggers warning in marctagstructure.pl

Bug 8714 - Poorly ordered and triggers warning in marctagstructure.pl

An array boundary check was after a comparison using the array.
By changing the logic which had " and ( $j < $cnt)" to be at the
beginning "( $j < $cnt ) and ", the warning is no longer shown
in the error log.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>