Fixes two aspects in SkPath to provide a fast path for drawing full ovals

1. When startAngle and SweepAngle vectors are coincident, existing
implementation returns a single point.  However, it should draw a
full circle if (sweepAngle - startAngle) % 360 == 0

2. when SkPath::arcTo(rect, 0, 360, true/false), the rendering path
should go to the fast path SkPath::addOval.