bug fixes from PVS Studio (static analysis)

  - Hal, please check out SkPDFCanon... was this unused?
  - Cary, please SkOpContour... is it right that allDone isn't necessary?
  - Brian, the rest?

Bug: chromium:805881

Change-Id: I7cbbcf44f4460a114f4ed2a59ed3856203049cdc
Reviewed-on: https://skia-review.googlesource.com/99960
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
6 files changed