Commit 993d66 addes support for displaying raised hands, but it
failed to take into account the possibility that the hand is already
raised when the user is first added.

We're already doing it in the receiver loop.

Doing that at the sample level suffers from too much delay
due to buffering in the samplebuilder.

This fixes an issue with out-of-order packet's start flag not
being correctly set in all cases.

If the stream was very short, we may not have created
a writer yet.  Write out packets even in that case.

Apparently the field has a different name than the HTML attribute.

Chromium 91 and later uses "AV1" instead of "AV1X".  Simulcast is
still broken.

Show the "hand-paper" symbol instead of the "circle" symbol while a
user is raising their hand.

(*webClient).action may be called with the group mutex taken,
and therefore cannot take the client mutex.

This prevents simulcast from being switched on when we enable
recording.

We now request a keyframe if we lose too many packets.

This version fixes issues with out-of-order packets.

This avoids a crash when a single frame was too large for the
samplebuilder.

Fix small typo

This makes for better error messages.