go/types, types2: add test case for missing return
The respective issue was fixed in types2 with CL 356189;
and the problem didn't exist in go/types. This CL simply
adds the test case to the type checkers as well.
For #49003.
Change-Id: Ib50ee8bb0ad21f2916f2b79d4f77593302899a3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/356411
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>