fix race condition when loading new chat

lib/widgets/room_chat.dart

@@ -90,13 +90,14 @@ class RoomChat extends HookConsumerWidget {
     }, [scrollController.hasClients]);
 
     useEffect(() {
-      if (scrollController.position.atEdge &&
+      if (scrollController.hasClients &&
+          scrollController.position.atEdge &&
           scrollController.position.pixels != 0) {
-        WidgetsBinding.instance.addPostFrameCallback((_) {
+        WidgetsBinding.instance.addPostFrameCallback(
-          if (scrollController.hasClients) {
+          (_) => scrollController.jumpTo(
-            scrollController.jumpTo(scrollController.position.maxScrollExtent);
+            scrollController.position.maxScrollExtent,
-          }
+          ),
-        });
+        );
       }
       return null;
     }, [controllerData]);