stdscan.c: clarify comment
stdscan.c: clarify comment

There is a reason rn_warn isn't checked in this particular case...

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