don't produce empty slugs

Change-Id: Ie7e882b559e05a5a3b33ab5e08611f84e448ef19
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/510417
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed