[sksg] Hoist empty-bounds check to base RenderNode

Empty-bounds nodes should never render anything.

TBR=

Change-Id: Iaa216a1d49a4a81054bcae19c1fff5a85e543c50
Reviewed-on: https://skia-review.googlesource.com/c/193690
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
5 files changed