BR 3392576: don't segfault on a bad %pragma limit
BR 3392576: don't segfault on a bad %pragma limit

Don't segfault on a bad %pragma limit. Instead treat a NULL pointer as
an empty string.

Reported-by: Ren Kimura <3fccf32a406f470e1a4490d6d5eead8c7b13e6c0@gmail.com>
Signed-off-by: H. Peter Anvin (Intel) <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm