Ticket 48745 - Matching Rule caseExactIA5Match indexes incorrectly values with upper cases
Description: Fixing a minor coverity defect introduced by #48745.
> Defect type: REVERSE_INULL
> plugin_mr.c:671: check_after_deref: Null-checking "pi" suggests that
> it may be null, but it has already been dereferenced on all paths
> leading to the check.
Moving the NULL check back to the original position.