fnmatch: avoid compiler warning

fnmatch: avoid compiler warning

cond ? (size_t) : (char* - char* + 1) varies in signedness, but
using 1LU coerces the latter half to unsigned math.

* lib/fnmatch_loop.c (NEW_PATTERN): Coerce addition to unsigned,
to silence compiler warning about mismatch signedness in ?:.
Reported by Robert Millan.

Signed-off-by: Eric Blake <ebb9@byu.net>