myql_common.c:gw_send_change_user_to_backend checks func.write for 0 and 1

mysql_client.c:gw_MySQLWrite_client is simply return dcb_write(dcb, queue);
The return codes are not the same of the code replaced, but they are not checked in the caller routines.

server/modules/protocol/mysql_common.c

@@ -986,7 +986,7 @@ int gw_send_change_user_to_backend(char *dbname, char *user, uint8_t *passwd, My
 
 	rv = dcb->func.write(dcb, buffer);
 
-	if (rv < 0)
+	if (rv == 0)
 		return 0;
 	else
 		return 1;