[BUGFIX canary] This fixes the output for not escaping `{{{x}}}`

This version of the fix is for canary, where things have been moved
around a bit. I'll submit a fix for Beta/Release too which is
essentially the same only in a different place.
`isNone` looks equivalent. I copied how other parts of Ember.js seemed to be doing it. Whenever in doubt I mimic how other people do it!