bugfix: messages: Fix crash when editing message.

When `realm_message_content_edit_limit_seconds` is None,
which means no time limit for editing message,
ZT crashes with `TypeError`.
This happens in Zulip cloud server.
Fixes #1467.

Author: Young-Lord

zulipterminal/ui_tools/messages.py

@@ -1045,12 +1045,12 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
             # the time limit. A limit of 0 signifies no limit
             # on message body editing.
             msg_body_edit_enabled = True
-            if self.model.initial_data["realm_message_content_edit_limit_seconds"] > 0:
+            edit_time_limit = self.model.initial_data[
+                "realm_message_content_edit_limit_seconds"
+            ]
+            if edit_time_limit is not None and edit_time_limit > 0:
                 if self.message["sender_id"] == self.model.user_id:
                     time_since_msg_sent = time() - self.message["timestamp"]
-                    edit_time_limit = self.model.initial_data[
-                        "realm_message_content_edit_limit_seconds"
-                    ]
                     # Don't allow editing message body if time-limit exceeded.
                     if time_since_msg_sent >= edit_time_limit:
                         if self.message["type"] == "private":