[skottie] Only apply effects to non-empty geometry stacks

TBR=
Change-Id: Iaafd63c787b72cdf83b21bd39cc10d01612e435d
Reviewed-on: https://skia-review.googlesource.com/97662
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed