Tighten pg_get_object_address argument checking

For publication schemas (OBJECT_PUBLICATION_NAMESPACE) and user
mappings (OBJECT_USER_MAPPING), pg_get_object_address() checked the
array length of the second argument, but not of the first argument.
If the first argument was too long, it would just silently ignore
everything but the first argument.  Fix that by checking the length of
the first argument as well.

I wouldn't be surprised if there were more holes like this in this area. 
  I just happened to find these while working on something related.