[Cleanup] Pre-set the variable to None in [p]cleanup before (#4931)

* [Cleanup] Handle missing message_id and reply

* Fix a new situation where we could end up with unwanted `None`

* I suck at this (style fix)

Co-authored-by: jack1142 <6032823+jack1142@users.noreply.github.com>

redbot/cogs/cleanup/cleanup.py

@@ -348,6 +348,7 @@ class Cleanup(commands.Cog):
 
         channel = ctx.channel
         author = ctx.author
+        before = None
 
         if message_id:
             try: