[AdaptiveTree] Fix spurious wakeups on TreeUpdateThread

[CastagnaIT]

Description

This problem was causing a delay on manifest updates due to wrong timings
and so weird buffering with some live streaming

was due to spurious wakeups where the previous wait_for was exiting early by returning std::cv_status::no_timeout
and so the while loop restarted, and the interval also each time restarted

Motivation and context

fix #1660

How has this been tested?

https://livesim2.dashif.org/livesim2/segtimeline_1/testpic_2s/Manifest.mpd
by looking at log timing between manifest downloads

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

[matthuisman]

yes to 21 backport please :)

[matthuisman]

will test tonight and report back

[matthuisman]

LGTM! 👍

[CastagnaIT]

good! yes i will backport and i will make new releases