go/types: fix panic when using multiple type arguments
Fix a panic caused by using type arguments without first unpacking.
This was noticed in the review of CL 300998, but unfortunately not yet
fixed.
Fixes #45635
Change-Id: I8ab1720f3e27a6002bc925f0eea943ec6f778341
Reviewed-on: https://go-review.googlesource.com/c/go/+/311669
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>