Bug fix for cull_line in SkDashPathEffect.

In cull_line we must also check if both points are the same. Otherwise we
fail the assert in the else "SkASSERT(dy && !dx)".

This is currently blocking the roll as it fails a webkit test.

BUG=skia:

Review URL: https://codereview.chromium.org/703783002
4 files changed