Don’t return error when coordinator is already in group. https://github.com/Koenkk/zigbee2mqtt/issues/1064

lib/zigbee.js

@@ -146,7 +146,7 @@ class Zigbee {
                 });
             } else {
                 logger.debug(`Coordinator is already in group '${groupID}'`);
-                callback(true);
+                callback(false);
             }
         });
     }