Because "contentText" is always present, PHP warnings were previously
generated for posts without text.
Existence of sub-property "runs" gets checked now to avoid this.
As YouTube doesn't provide precise dates for community posts, an
increasing multiple of 60 seconds is subtracted from each timestamp.
This ensures that the original order is always preserved, even if there
are multiple posts with the same date (e.g. "1 month ago").
