Revert "Don't return end from /messages if there are no more events (matrix-org#12903)"

This reverts commit c4f548e.

This is because Tchap clients currently rely on this bug for message
pagination.

Author: babolivier

synapse/handlers/pagination.py

@@ -526,29 +526,18 @@ async def get_messages(
 
             next_token = from_token.copy_and_replace(StreamKeyType.ROOM, next_key)
 
-        # if no events are returned from pagination, that implies
-        # we have reached the end of the available events.
-        # In that case we do not return end, to tell the client
-        # there is no need for further queries.
-        if not events:
-            return {
-                "chunk": [],
-                "start": await from_token.to_string(self.store),
-            }
+        if events:
+            if event_filter:
+                events = await event_filter.filter(events)
 
-        if event_filter:
-            events = await event_filter.filter(events)
-
-        if not use_admin_priviledge:
-            events = await filter_events_for_client(
-                self._storage_controllers,
-                user_id,
-                events,
-                is_peeking=(member_event_id is None),
-            )
+            if not use_admin_priviledge:
+                events = await filter_events_for_client(
+                    self._storage_controllers,
+                    user_id,
+                    events,
+                    is_peeking=(member_event_id is None),
+                )
 
-        # if after the filter applied there are no more events
-        # return immediately - but there might be more in next_token batch
         if not events:
             return {
                 "chunk": [],