Ensure provider hook calls don't crash because of invalid command line arguments

[tolbrino]

Normally the CLI arguments are intended for the provider which is called directly. When these are forwarded to other providers through hooks things might break.

[ferd]

This is a good fix, but we'll need to add a test for this before we merge it. This is core dispatching functionality we shouldn't change without repeatable validation.

[tsloughter]

ping @tolbrino

[tolbrino]

ping @tolbrino

I got blocked by trying to get a test working, but to no avail. I will take a look again some time later this week.