regexpSimplify gives an incorrect simplification for (foo|).

[csilvers]

For this file:

package test
import "regexp"
var _ = regexp.MustCompile(`(a|)`)

gocritic gives this output:

% go run github.com/go-critic/go-critic/cmd/gocritic@latest check --enable '#style' /tmp/test.go
/tmp/test.go:5:28: regexpSimplify: can re-write `(a|)` as `(|?)`

The simplification presumably was meant to be (a)?.

Another example is the string (?:\.(\d+)|), which gocritic wants to simplify to (?:|?). Which may give some idea about what it's matching incorrectly here.