Ensure Embed description is not Embed.Empty before stripping
Sentry Issue: [BOT-6K](https://sentry.io/organizations/python-discord/issues/1764434612/?referrer=github_integration)

It's a special value instead of simply an empty string, so trying to strip it may fail. Other code should also be reviewed to ensure it can't fail for similar reasons.

```
AttributeError: '_EmptyEmbed' object has no attribute 'strip'
  File "discord/client.py", line 312, in _run_event
    await coro(*args, **kwargs)
  File "bot/cogs/help_channels.py", line 719, in on_message_delete
    if not await self.is_empty(msg.channel):
  File "bot/cogs/help_channels.py", line 733, in is_empty
    return self.match_bot_embed(msg, AVAILABLE_MSG)
  File "bot/cogs/help_channels.py", line 443, in match_bot_embed
    return message.author == self.bot.user and embed.description.strip() == description.strip()

Unhandled exception in on_message_delete.
```
diff --git a/bot/cogs/help_channels.py b/bot/cogs/help_channels.py
index 0c8cbb41..e0fd0665 100644
--- a/bot/cogs/help_channels.py
+++ b/bot/cogs/help_channels.py
@@ -428,8 +428,11 @@ class HelpChannels(commands.Cog):
         if not message or not message.embeds:
             return False
 
-        embed = message.embeds[0]
-        return message.author == self.bot.user and embed.description.strip() == description.strip()
+        bot_msg_desc = message.embeds[0].description
+        if bot_msg_desc is discord.Embed.Empty:
+            log.trace("Last message was a bot embed but it was empty.")
+            return False
+        return message.author == self.bot.user and bot_msg_desc.strip() == description.strip()
 
     @staticmethod
     def is_in_category(channel: discord.TextChannel, category_id: int) -> bool:
['bot/cogs/help_channels.py']