Fix underlying issue causing crbug.com/348821.

Fix underlying issue causing crbug.com/348821.

SkDashPathEffect refuses to flatten itself if it thinks it's a no-op.  This
messes with the assumption that flattening a non-NULL effect and then
unflattening from those bytes produces a non-NULL effect.  I'd rather make that
assumption always be true than save a few bytes for rare nonsense path effects.

BUG=348821
R=reed@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/189643002

git-svn-id: http://skia.googlecode.com/svn/trunk@13701 2bbb7eff-a529-9590-31e7-b0007b416f81