Don't call iterator.return() on normal exit
Don't call iterator.return() on normal exit

Match the behavior of the for-of loop, which does not call return() if
next() has returned done.  Only call on early-exit.

Signed-off-by: Kevin Locke <ffb4761cba839470133bee36aeb139f58d7dbaa9@kevinlocke.name>

kevinoid/appveyor-status,kevinoid/appveyor-status,kevinoid/appveyor-status