model: Replace the dummy message on receiving a new message.

Co-authored-by: Sumanth V Rao <sumanthvrao@gmail.com>

Author: Niloth-p

tests/model/test_model.py

@@ -1913,6 +1913,7 @@ def test__handle_message_event_with_Falsey_log(
         mocker.patch(MODEL + "._update_topic_index")
         mocker.patch(MODULE + ".index_messages", return_value={})
         self.controller.view.message_view = mocker.Mock(log=[])
+        self.controller.is_in_empty_narrow = False
         create_msg_box_list = mocker.patch(
             MODULE + ".create_msg_box_list", return_value=["msg_w"]
         )
@@ -1932,6 +1933,7 @@ def test__handle_message_event_with_valid_log(self, mocker, model, message_fixtu
         mocker.patch(MODEL + "._update_topic_index")
         mocker.patch(MODULE + ".index_messages", return_value={})
         self.controller.view.message_view = mocker.Mock(log=[mocker.Mock()])
+        self.controller.is_in_empty_narrow = False
         create_msg_box_list = mocker.patch(
             MODULE + ".create_msg_box_list", return_value=["msg_w"]
         )
@@ -1954,6 +1956,7 @@ def test__handle_message_event_with_flags(self, mocker, model, message_fixture):
         mocker.patch(MODEL + "._update_topic_index")
         mocker.patch(MODULE + ".index_messages", return_value={})
         self.controller.view.message_view = mocker.Mock(log=[mocker.Mock()])
+        self.controller.is_in_empty_narrow = False
         mocker.patch(MODULE + ".create_msg_box_list", return_value=["msg_w"])
         model.notify_user = mocker.Mock()
         set_count = mocker.patch(MODULE + ".set_count")
@@ -2097,6 +2100,7 @@ def test__handle_message_event(
         (
             self.controller.view.left_panel.is_in_topic_view_with_stream_id.return_value
         ) = False
+        self.controller.is_in_empty_narrow = False
         model.notify_user = mocker.Mock()
         model.narrow = narrow
         model.recipients = recipients

zulipterminal/model.py

@@ -1742,6 +1742,9 @@ def _handle_message_event(self, event: Event) -> None:
                 msg_w = msg_w_list[0]
 
             if self.current_narrow_contains_message(message):
+                if self.controller.is_in_empty_narrow:
+                    del msg_log[0]
+                    self.controller.is_in_empty_narrow = False
                 msg_log.append(msg_w)
 
             self.controller.update_screen()