fix(JitsiConference.leave): reject in case of a timeout
fix(JitsiConference.leave): reject in case of a timeout

JitsiConference shouldn't lie that the leave() was successful when it
was not.

jiyeyuran/lib-jitsi-meet,jitsi/lib-jitsi-meet,jitsi/lib-jitsi-meet,damencho/lib-jitsi-meet