New test for another error case in DepositScriptAddress

> And as I replied to you before, it won't because checkManagerError()
> uses the comma ok idiom, which accounts for that.

I was wrong about the error that would be sent back. It's still a bug:

In your branch (gsalgado/vp) change line 411 in pool.go and insert: "return nil, nil"
Your test passes.

> The testName argument in checkManagerError() is meant for 
> table-driven tests, which is not the case here.

Not clear to me from reading the checkManagerError function or the documentation, but I'll trust you here. I would ask someone at conformal to clarify that in the documentation.