msglist: Autofocus compose box only when the whole history is empty

Previously, if the initial batch came up empty, then the history was
considered empty too. But now, the initial batch could be empty
because of the messages in muted conversations while there may still be
other messages in history.

Author: sm-sayedi

lib/widgets/message_list.dart

@@ -895,7 +895,7 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
     model.fetchInitial();
   }
 
-  bool _prevFetched = false;
+  bool _hasAutofocused = false;
 
   void _modelChanged() {
     // When you're scrolling quickly, our mark-as-read requests include the
@@ -945,14 +945,14 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
       _fetchMoreIfNeeded(scrollController.position);
     });
 
-    if (!_prevFetched && model.fetched && model.messages.isEmpty) {
-      // If the fetch came up empty, there's nothing to read,
-      // so opening the keyboard won't be bothersome and could be helpful.
+    if (model.messages.isEmpty && model.haveNewest && model.haveOldest && !_hasAutofocused) {
+      // If there are no messages to show in the whole history,
+      // opening the keyboard won't be bothersome and could be helpful.
       // It's definitely helpful if we got here from the new-DM page.
       MessageListPage.ancestorOf(context)
         .composeBoxState?.controller.requestFocusIfUnfocused();
+      _hasAutofocused = true;
     }
-    _prevFetched = model.fetched;
   }
 
   /// Find the range of message IDs on screen, as a (first, last) tuple,