Bad error for closure actions wrapping missing functions.

[rwjblue]

When using closure actions to wrap a function in the current context, if the function that you provide is undefined you receive a very non-helpful error message at the time you invoke the closure wrapped action (i.e. this.attrs.blah()).

Example snippet:

{{#foo-bar blah=(action somethingThatIsUndefined)}}
  Click Me!
{{/foo-bar}}

Invoking blah via this.attrs.blah() throws the following error:

Cannot read property 'apply' of undefined at Object.closureAction [as blah] (http://builds.emberjs.com/canary/ember.debug.js:22364:22)
    at click (necodu.js:20:16)
    at _emberRuntimeSystemObject.default.extend.trigger (http://builds.emberjs.com/canary/ember.debug.js:43201:23)
    at superWrapper [as trigger] (http://builds.emberjs.com/canary/ember.debug.js:21493:22)
    at Object._emberMetalMerge.default.handleEvent (http://builds.emberjs.com/canary/ember.debug.js:44108:21)

Demo: http://rwjblue.jsbin.com/necodu/edit?html,js,output