io/gzio: Bail if gzio->tl/td is NULL

io/gzio: Bail if gzio->tl/td is NULL

This is an ugly fix that doesn't address why gzio->tl comes to be NULL.
However, it seems to be sufficient to patch up a bunch of NULL derefs.

It would be good to revisit this in future and see if we can have
a cleaner solution that addresses some of the causes of the unexpected
NULL pointers.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Patch-Name: 2021-02-security/080-io-gzio-Bail-if-gzio-tl-td-is-NULL.patch