preproc: fix list iteration in the case of expand_indirect()
preproc: fix list iteration in the case of expand_indirect()

Linked lists where an element may be deleted or substituted during
processing can be subtle to deal with.  Fix the iteration conditions
in this particular case.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

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