Fixes for call state machine
Fixes for call state machine

 * Set 'connecting' state before sending answer, otherwise it can
   race with ICE connecting
 * Ignore completed ice connection state: connected is what we care about
 * Null-check remotestream when stopping media
 * Comments

matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk