fix circle dash

Thin conic dashes are treated as lines both if the
curvature is detected as zero, and if the midpoint
is close enough to the control point.

To fix:
Halve the midpoint to control point magic number.
Use quad max curvature as a placeholder for conic
max curvature.

R=reed@google.com,fmalita@chromium.org
Bug:843966
Change-Id: Ide43bef8767c03670ffd19fdc38c191d6e2332f3
Reviewed-on: https://skia-review.googlesource.com/c/129243
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Cary Clark <caryclark@skia.org>
2 files changed