fix: pass error to ext for prefixed subcommand checking

[AstreaTSS]

What type of pull request is this?

• Non-breaking code change
• Breaking code change
• Documentation change/addition
• Tests change

Description

So I forgot to pass the e here... or maybe the e was added after this code was made, and someone forgot to put it here. Either way, this PR passes the error for extension error handlers for prefixed subcommand checking.

Changes

• I, uh, passed an e. Just look at the diff it isn't complex--

Checklist

• I've formatted my code with Black
• I've ensured my code works on Python 3.10.x
• I've tested my code