Guard GrRadialGradientLayout::TestCreate against Empty shaders

With certain degenerate params (decal mode and a very small radius), we
could produce an SkShader that's an instance of SkEmptyShader, which
then failed to create an FP.

Bug: skia:8660 skia:8860 skia:8982
Change-Id: I47142572cd0c75d15c6ee1e66e3140786431371f
Reviewed-by: Herb Derby <>
Reviewed-by: Michael Ludwig <>
Commit-Queue: Brian Osman <>
2 files changed