Cleanup buffer-helper functions and remove nested try-catch statements

[robwalch]

This PR will...

Cleanup buffer-helper functions and remove nesting try-catch statements

Why is this Pull Request needed?

• Fixes case where getBuffered can return undefined (media.buffered if not defined should fallthough to empty TimeRange)
• isBuffered and bufferInfo no longer need try-catch blocks because they don't throw and neither do their sub-routines

Are there any points in the code the reviewer needs to double check?

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md