message_edit: Fix false sub/unsub bookend on using a near link.

We were not setting the `historical` flag correctly for
messages fetched via `json_fetch_raw_message` when used didn't
have any UserMessage.

Extended relevant tests to fetch check message flags too.

zerver/tests/test_message_edit.py

@@ -322,6 +322,7 @@ def test_fetch_message_from_id(self) -> None:
         self.assert_json_success(result)
         self.assertEqual(result.json()["raw_content"], "Personal message")
         self.assertEqual(result.json()["message"]["id"], msg_id)
+        self.assertEqual(result.json()["message"]["flags"], [])
 
         # Send message to web public stream where hamlet is not subscribed.
         # This will test case of user having no `UserMessage` but having access
@@ -335,6 +336,7 @@ def test_fetch_message_from_id(self) -> None:
         self.assert_json_success(result)
         self.assertEqual(result.json()["raw_content"], "web-public message")
         self.assertEqual(result.json()["message"]["id"], web_public_stream_msg_id)
+        self.assertEqual(result.json()["message"]["flags"], ["read", "historical"])
 
         # Spectator should be able to fetch message in web public stream.
         self.logout()
@@ -416,6 +418,7 @@ def test_fetch_raw_message_spectator(self) -> None:
         result = self.client_get("/json/messages/" + str(web_public_stream_msg_id))
         self.assert_json_success(result)
         self.assertEqual(result.json()["raw_content"], "web-public message")
+        self.assertEqual(result.json()["message"]["flags"], ["read"])
 
         # Verify LIMITED plan type does not allow web-public access.
         do_change_realm_plan_type(user_profile.realm, Realm.PLAN_TYPE_LIMITED, acting_user=None)

zerver/views/message_edit.py

@@ -205,6 +205,8 @@ def json_fetch_raw_message(
     else:
         if user_message:
             flags = user_message.flags_list()
+        else:
+            flags = ["read", "historical"]
         allow_edit_history = maybe_user_profile.realm.allow_edit_history
 
     # Security note: It's important that we call this only with a