fix bookmaker check for enum size

upcoming enum size change in public header
exposed missing check in bookmaker

TBR=mtklein@google.com

Bug: skia:6818
Change-Id: Idaf108cb36283805dd0ff8e709646325c78a9d66
Reviewed-on: https://skia-review.googlesource.com/146769
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
1 file changed