fix fuzzing empty contours squirrelly cubics

The fuzzer triggered relatively new code that
missized the split cubic array, i.e., if a cubic
is split in three places it makes four cubics.

The fuzzer triggered other relative new code
that permits a contour to be empty. This happens
when a line crosses over itself but doesn't
enclose anything.

R=kjlubick@google.com
BUG=skia:6061

Change-Id: I0c04d0d390ff1092f7b3bb28ebbfca517451f497
Reviewed-on: https://skia-review.googlesource.com/6223
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed