fix jpegload from empty buffer
fix jpegload from empty buffer

could try to read a couple of non-existent bytes before failing ... now we
inject an EOI marker

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