fix(ngAnimate): fix cancelChildAnimations throwing exception

[gregolsky]

fix ngAnimate throwing exception in cancelChildAnimations on deletion of
element (ngAnimate's leave decorator) of repeated element when using
ng-include on this element.

Closes #4548

[mary-poppins]

Thanks for the PR!

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Thanks again for your help!

[gregolsky]

My real name: Grzegorz Lachowski

[matsko]

Testing the code against a CI server now.

[gregolsky]

Not sure if I've done something wrong, but it says "The Travis CI build failed". Anything I need to do about it?

[matsko]

Travis sometimes breaks. I'm testing it against the custom AngularJS CI server right now.

[matsko]

Landed as b9557b0

[matsko]

Great work!

[gregolsky]

Thanks for your help :) This was fun!