Fix X509_ALGOR_set0() usage in rsa_alg_set_oaep_padding()

Fix X509_ALGOR_set0() usage in rsa_alg_set_oaep_padding()

Replace X509_ALGOR_set0() with X509_ALGOR_set0_by_nid(). This way there
is no missing error checking for OBJ_nid2obj() and no nested functions.
Slightly more importantly, this plugs two long standing potential leaks
in this function (or previously rsa_cms_encrypt()) due to missing error
checking: in the unlikely event that X509_ALGOR_set0() failed, astr/ostr
would leak.

ok jsing