EXT-7371 FIXED Improved new state handling in p2p Voice channel to process...

EXT-7371 FIXED Improved new state handling in p2p Voice channel to process session leave event correctly.
Reason:
* when user leave a p2p voice session himself the session's voice channel is marked as "ignore next leave session event"
* but when he re-starts the voice session the channel stays in "ignore next leave session event" state.
So, when an other p2p participant ends call this voice channel is not deactivated because of this flag.

Fix: reset "ignore next leave session event" flag to FALSE when viewer is joining p2p voice session.

Reviewed by Aimee Walton at https://codereview.productengine.com/secondlife/r/418/

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branch : product-engine