OpenSSL: Write PKCS#12 extra cert errors into debug log

OpenSSL: Write PKCS#12 extra cert errors into debug log

Commit de2a7b796d82d92120aa9532450863f503e1885a ('OpenSSL: Use
connection certificate chain with PKCS#12 extra certs') added a new
mechanism for doing this with OpenSSL 1.0.2 and newer. However, it did
not poinr out anything in debug log if SSL_add1_chain_cert() failed. Add
such a debug print and also silence static analyzer warning on res being
stored without being read (since the error case is ignored at least for
now).

Signed-off-by: Jouni Malinen <j@w1.fi>