fix out of bounds write in radiance
fix out of bounds write in radiance

It was using a fixed 64-byte stack buffer for the RHS of format lines.
Lines can be MAXLINE (2048) chars, so a long line could overflow. If we
use MAXLINE for the small buffer as well, we are guaranteed to not
overflow.

thanks HongxuChen

See https://github.com/jcupitt/libvips/issues/1039

jcupitt/libvips,jcupitt/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,jcupitt/libvips,lovell/libvips,lovell/libvips