audio-mode: don't change the mode unless there is no active conference
audio-mode: don't change the mode unless there is no active conference

If a new conference is joined and as a result the current one is terminated,
don't ever attempt to set the audio mode.

gpolitis/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet