cc: Allow serialization failure for paths.

We currently assume that a path will always serialize to a non-zero size,
and so we should always get a valid path at deserialization. But SkPath
may return a zero size indicating that the given path can not be
serialized. Account for that and just bail out serializing this path.

R=enne@chromium.org

Bug: 924042
Change-Id: I467003ea90efd5915b24b032d079bde2c3c5cacd
Reviewed-on: https://chromium-review.googlesource.com/c/1481084
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634901}