Fix assert in FuzzNicePath

Change-Id: Ic92ae7fd7087a188a4a3ca523a75808f7ef06eae
Bug: oss-fuzz:506737090
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1229176
Commit-Queue: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Kaylee Lubick <kjlubick@google.com>