Don't try to fire actions that don't exist

Those happen frequently in Lotus, for example sometimes when closing ticket tabs.

![](https://f.cloud.github.com/assets/279376/1476890/781eb5be-4651-11e3-8848-a2d44c9a36be.png)

Fix ported from https://github.com/emberjs/ember.js/commit/aafb5eb5693dccf04dd0951385b4c6bb6db7ae46.

Ember 1.0 has a much complex way of fixing the problem, but the one above was their first solution I think, and should be good enough for us while we migrate to Ember 1.0.

/cc @jamesarosen @shajith @kruppel