go/types: don't panic if targs don't match tparams when substituting
Invalid code may produce instances where the number of type arguments
does not match the number of type parameters. Such code will cause an
error, but should not cause a panic when substituting in those invalid
instances.
Fixes #48529
Change-Id: Ie5ff5ace55921540a7224cc5022ef9ff7649361a
Reviewed-on: https://go-review.googlesource.com/c/go/+/351337
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>