[skottie] Harden interpolation checks for shapes

The "closed" shape property cannot be interpolated -- so ensure we catch
different values in interpolation pre-checks.

Bug: skiai:8264
Change-Id: If2c7e09c1227b0013acba3833c314e0646715d52
Reviewed-on: https://skia-review.googlesource.com/147967
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
3 files changed