BR 1880905: make sure we have enough zero-padding data for 'DO'
BR 1880905: make sure we have enough zero-padding data for 'DO'

When using DO with a string that was too short, we would run off the
end of an all-zero buffer.  Make sure the buffer is long enough.

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