preproc.c: get_ctx() can return NULL...
preproc.c: get_ctx() can return NULL...

Handle the case where we would attempt to look up a possible local
context just to find that one doesn't exist.

Distrotech/nasm,letolabs/nasm,letolabs/nasm,turingstudio/nasm,Distrotech/nasm,Distrotech/nasm,projedi/nasm,letolabs/nasm,techkey/nasm,Distrotech/nasm,turingstudio/nasm,techkey/nasm,projedi/nasm,projedi/nasm,projedi/nasm,techkey/nasm,projedi/nasm,techkey/nasm,techkey/nasm,turingstudio/nasm,turingstudio/nasm