fix buffer overflow in radiance read
fix buffer overflow in radiance read

old-style RLE images could overflow the output buffer if incorrectly coded

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

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