Update getObserverFacade.js

Added a missing 'else'. Fixes a bug where cancelling a pattern observer would (additionally) throw an error.
Merge branch 'patch-1' of https://github.com/Writhe/ractive into Writhe-patch-1
add tests from http://jsfiddle.net/Writhe/CQ92s/
Merge branch 'Writhe-patch-1' into dev