update processing,customer and staff

lib/pages/chat/model/message_model.dart

@@ -38,7 +38,7 @@ class MessageModel extends BaseModel {
   }
 
   Future<void> load() async {
-    if (prevSnap == null) return;
+    // if (prevSnap == null) return;
     Query _query =
         prevSnap != null ? query.startAfterDocument(prevSnap!) : query;
     QuerySnapshot snapshot =
@@ -62,8 +62,8 @@ class MessageModel extends BaseModel {
 
     listener = FirebaseFirestore.instance
         .collection("$user_collection/$userID/$messages_collection")
-        .endBeforeDocument(snap)
         .orderBy('date', descending: true)
+        .endBeforeDocument(snap)
         .snapshots(includeMetadataChanges: true)
         .listen((qs) {
       qs.docChanges.forEach((c) {