namemap: change ossl_namemap_empty() to do what the documentation says.

namemap: change ossl_namemap_empty() to do what the documentation says.

The function is documented as returning 1 when passed a NULL argument.
Instead it core dumps.  Added a unit test for this.

Additionally, a performance improvement is incorporated.  The namemap
max_number field is only ever compared against zero and incremented.
The zero comparison grabs a lock specifically for this check.  This change
uses TSAN operations instead if they are available.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12181)