Fixed an error when deleting a catagory

Author: Taaku18

bot.py

@@ -438,6 +438,9 @@ async def on_guild_channel_delete(self, channel):
         if mod == self.user:
             return
 
+        if not isinstance(channel, discord.TextChannel):
+            return
+
         thread = await self.threads.find(channel=channel)
         if not thread:
             return

core/thread.py

@@ -503,7 +503,7 @@ async def _find_from_channel(self, channel):
             if user_id in self.cache:
                 return self.cache[user_id]
 
-            recipient = self.bot.get_user(user_id)  # this could be None
+            recipient = self.bot.get_user(user_id)
             if recipient is None:
                 self.cache[user_id] = thread = Thread(self, user_id, channel)
             else: