Update ngClass.js

[trevordowdle]

I don't know if this was intended, but I don't think the code was comparing the indexes correctly and it was causing some weird behavior when using the ng-class-even and ng-class-odd directives.

See the following plunkr for an example of the bug. http://plnkr.co/edit/VAi6DB0QdWRutNGnVdSL?p=preview

Select the Red Radio button option to see that when switching classes on rows the classes are not always switched properly.

[mary-poppins]

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

• Uses the issue template (#7479)

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!

[petebacondarwin]

@trevordowdle - thanks for this PR. Could you create a unit test that demonstrates the bug and sign the CLA please?

[trevordowdle]

I just signed the CLA.

I would be happy to create a unit test. However my wife is pregnant and in the Hospital getting ready for labor and I need get there right now. So It may be a 2-3 days but as soon as I have it, i'll get it to you.

What should I do with the unit test once created? Is there a place in the repository you store unit tests?

Thanks

[btford]

@trevordowdle no rush. and congrats. :)

You could add a test here: https://github.com/angular/angular.js/blob/master/test/ng/directive/ngClassSpec.js

See the development docs for running the tests:
https://docs.angularjs.org/misc/contribute#running-the-unit-test-suite

[shahata]

This is indeed a bug, I already have a PR for this: #7262

[btford]

I'm closing this in favor of #7262. Still, thank you @trevordowdle!