Playback stops with bad cue times on IE/Edge

[joeyparrish]

@baseballbrad3 reports in #312 (comment):

We have some poorly formatted subtitles that would appear to have the same start and end times (or a duration of zero). When IE/Edge try to create a new TextTrackCue, the object creation throws an exception of "Syntax Error" and halts all playback.

Now, we certainly are to blame for the malformed VTT track, but I was wondering if it'd make sense to check that end > start prior to creation of the Cue.

We'd absolutely like to fix them, and (long term) we plan to, but unfortunately for us, it's difficult to go back and fix them.

From a user's perspective, if a video was unplayable, I'd be pretty upset. If a line here and there were dropped from the subtitles, I'd be a bit confused but would be less impacted. Certainly having some log messages when the subtitle is loaded would help identify the problem when a complaint came in.

[joeyparrish]

@baseballbrad3, this has been verified via integration tests running on IE11. Let us know if there are any issues with this change in your own app.