Fix SimplifyStringSet() for really reals. And the test.

Change-Id: I4c211f8f4eea0a5b2afcbb85319a8467b7f29398
Reviewed-on: https://code-review.googlesource.com/c/re2/+/42518
Reviewed-by: Paul Wankadia <junyer@google.com>
2 files changed