Fix error raised when recipient is not cached and reacts to reactions in DM channel.

Author: Jerrie-Aries

bot.py

@@ -1153,7 +1153,7 @@ async def on_typing(self, channel, user, _):
 
     async def handle_reaction_events(self, payload):
         user = self.get_user(payload.user_id)
-        if user.bot:
+        if user is None or user.bot:
             return
 
         channel = self.get_channel(payload.channel_id)