pki: Fix resource leak on error.

src/pki_crypto.c

@@ -850,6 +850,7 @@ ssh_string pki_publickey_to_blob(const ssh_key key)
             e = make_ecpoint_string(EC_KEY_get0_group(key->ecdsa),
                                     EC_KEY_get0_public_key(key->ecdsa));
             if (e == NULL) {
+                ssh_buffer_free(buffer);
                 return NULL;
             }