Abort vjs.trigger when "elem" param is invalid

[ghost]

Related to #1484
vjs.hasData throws a fit (exception) and aborts the whole process when the "elem" param of vjs.trigger is null or undefined.
That easily broke testing with Karma.

It was discovered in Karma-jasmine tests LoveIsGrief/videojs-soundcloud/test/unit/main-spec.coffee#72. A new player is created in the beforeEach and disposed of in afterEach.

This is just treating the symptom, not cause, but I need it nonetheless to run the tests.

Cheers

[heff]

I'm cautious about a fix like this because it would hide the error, making it more difficult to see potential memory leaks and failures to clean up intervals and listeners. @mmcc is working on a fix for the same issue that cleans up all player-related timeouts and intervals on dispose. I also just merged in #1588 which should help with these issues to some degree. I'd like to see if those don't stop this from happening first.

[heff]

Going to close this but will reopen if we need to go this direction.