Improve do-while test in CanExitWithoutReturningValue.

This put the coverage for do-while loops on par with for loops.

Change-Id: I53e0d733edd02a6a139792a8d74c68116453e5ff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/385500
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
2 files changed