Fix OBJ_create() to tolerate a NULL sn and ln

In 1.0.2 and before OBJ_create() allowed the sn or ln parameter to be NULL.
Commit 52832e47

 changed that so that it crashed if they were NULL.

This was causing problems with the built-in config oid module. If a long
name was provided OBJ_create() is initially called with a NULL ln and
therefore causes a crash.

Fixes #3733

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3753)