Support for Wrapping Errors with defer

[qawatake]

It would be great if the tool could also check cases where errors are wrapped using defer, such as with golang.org/x/pkgsite/internal/derrors.Wrap.

func wrap(errp *error) {}

func f() (err error) {
	defer wrap(&err)
	err = do()
	if err != nil {
		return nil // want "error is not nil"
	}
	return nil
}

Would it be possible to add support for this scenario?