Correctly stroke zero length segments in multi-contour paths

Bug: skia:
Change-Id: I959287780ef94a258a6746132f3acb9f90e6c6cc
Reviewed-on: https://skia-review.googlesource.com/21863
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed