refactor: messages: Allow datetime field of current message to be empty.

Author: Niloth-p

zulipterminal/ui_tools/messages.py

@@ -683,7 +683,8 @@ def main_view(self) -> List[Any]:
             "recipients": recipient_header is not None,
             "author": message["this"]["author"] != message["last"]["author"],
             "24h": (
-                message["last"]["datetime"] is not None
+                message["this"]["datetime"] is not None
+                and message["last"]["datetime"] is not None
                 and ((message["this"]["datetime"] - message["last"]["datetime"]).days)
             ),
             "timestamp": (