Fix GrAAConvexTessellator trying to fan a 0 point ring

This prevents accessing off an empty array.

Bug: chromium:830038
Change-Id: I5ad019d56659c667564efc498dcef7fb112da4af
Reviewed-on: https://skia-review.googlesource.com/123800
Commit-Queue: Adrienne Walker <enne@chromium.org>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Adrienne Walker <enne@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed