asn1_item_embed_new(): if locking failed, don't call asn1_item_embed_free()

asn1_item_embed_free() will try unlocking and fail in this case, and
since the new item was just allocated on the heap, free it directly
with OPENSSL_free() instead.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/4579)