Actually set the tlscert conn reference

Previously it was always NULL

src/tls_gnutls.c

@@ -422,6 +422,8 @@ static int _tls_verify(gnutls_session_t session)
             return -1;
         }
 
+        tlscert->conn = tls->conn;
+
         if (tls->conn->certfail_handler(tlscert, (char *)out.data) == 0) {
             xmpp_tlscert_free(tlscert);
             gnutls_x509_crt_deinit(cert);

src/tls_openssl.c

@@ -540,6 +540,8 @@ static int _tls_verify(int preverify_ok, X509_STORE_CTX *x509_ctx)
     if (!tlscert)
         return 0;
 
+    tlscert->conn = conn;
+
     strophe_debug(conn->ctx, "tls", "preverify_ok:%d\nSubject: %s\nIssuer: %s",
                   preverify_ok, tlscert->elements[XMPP_CERT_SUBJECT],
                   tlscert->elements[XMPP_CERT_ISSUER]);