HlsMediaPlaylist.hasProgramDateTime is false when program date time is at epoch 0

I noticed that `HlsMediaPlaylist.hasProgramDateTime` is set to `false` for some streams that actually have a `#EXT-X-PROGRAM-DATE-TIME` tag.
To be more specific, the property is set `false` if the date time is set to epoch 0 (i.e. `#EXT-X-PROGRAM-DATE-TIME:1970-01-01T00:00:00.000Z`). As an effect the `Window.windowStartTimeMs` will be set to "unset".

Before filing a bug report I want to check with you if this is intentional for some reason or indeed a bug. Also maybe I am missing some detail of the HLS spec, but to my understanding the program date time could be basically any timestamp.