[AdaptiveTree] IsLastSegment return false if period is the last one

[CastagnaIT]

Description

PR #1586 change set the duration to all periods
this has lead to a different behaviour of AdaptiveTree::IsLastSegment

seem there is no a specific rule that dash use to signal a end of live playback
therefore we continue to insert segments until the downloads fail

Motivation and context

fix #1614 at least for dash case (hls should be not related)

How has this been tested?

Dash live inserts, single period:
http://daserstedash.akamaized.net/dash/live/2103597/daserste/dvbt2/manifest.mpd (germany geolock)
Dash live inserts, multiple periods: (at period change segments (numbers) downloaded must be exact)
https://livesim2.dashif.org/livesim2/ato_10/testpic_2s/Manifest.mpd

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• I have read the Contributing document
• My code follows the Code Guidelines of this project
• My change requires a change to the Wiki documentation
• I have updated the documentation accordingly