Fixes edgecase bug not captured by last CL.
Fixes edgecase bug not captured by last CL.

BUG=skia:2930
TBR=jcgregorio

Review URL: https://codereview.chromium.org/780223006

Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot