Fix invalid `return` in callback definition.

Current spec status: 460 examples, 0 failures in 1.79 seconds.
Rewrite callback to eliminate early break/return.

Current spec status: 460 examples, 0 failures in 2.68 seconds.
Merge pull request #9 from sleepingkingstudios/fix-callback-return

Rewrite callback to eliminate early break/return.