[skottie] Handle empty lines in Shaper
[skottie] Handle empty lines in Shaper

SkShaper doesn't seem to like empty inputs.

TBR=
Change-Id: Iace3eef389051dcce229ed4ac6897344770d19c3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/224190
Reviewed-by: Florin Malita <a8262bf13ea8c26821e91ea9bca6740a77c96dcd@chromium.org>
Commit-Queue: Florin Malita <a8262bf13ea8c26821e91ea9bca6740a77c96dcd@chromium.org>
Auto-Submit: Florin Malita <a8262bf13ea8c26821e91ea9bca6740a77c96dcd@chromium.org>

HalCanary/skia-hc,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia