fix(chat): catch exception when handling bot message

app/router/chat/banchobot.py

@@ -81,11 +81,13 @@ class Bot:
         if handler is None:
             return
         else:
+            try:
                 res = handler(user, args, session, channel)
                 if asyncio.iscoroutine(res):
                     res = await res
                 reply = res  # type: ignore[assignment]
-
+            except Exception:
+                reply = "Unknown error occured."
         if reply:
             await self._send_reply(user, channel, reply, session)