Make GCM providers more generous about fetching IVs

Make GCM providers more generous about fetching IVs

The current check for iv_gen and iv_gen_rand only lets you fetch
the IV for the case when it was set internally.  It might also make
sense to fetch the IV if one was set at cipher-context creation time,
so switch to checking the iv_state, which should be enough to ensure
that there is valid data in the context to be copied out.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/12233)