In iOS 13 if the call is not unmuted when we report it to the system as started,
an action to unmute it is dispatched automagically. Thanks, Apple.

So, delay synchronizing the muted state until the conference is started (after
the join action). This creates a small window for de-synchronization, but it's
very short and it seems unavoidable.

This change is only applied to operating systems built by the fruit company in
Cupertino.