io/gzio: Abort early when get_byte() reads nothing

io/gzio: Abort early when get_byte() reads nothing

This isn't intended to be a functional change, but it makes a lot of failures a lot
faster, which is extremely helpful for fuzzing.

Without this change, we keep trying and trying to read more bytes into our buffer,
never being able to (read always returns 0) and so we just return old buffer contents
over and over until the decompression process fails some other way.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>