Assert that a property definition cache entry is the first

Assert that a property definition cache entry is the first

When adding a property definition cache entry for a given property query
string we add an assert that we are not replacing an existing entry. If we
are then that indicates a bug in the caller.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18458)