fix(xmpp.js): logic around constant MUC nicknames
fix(xmpp.js): logic around constant MUC nicknames

adambowles/lib-jitsi-meet,jiyeyuran/lib-jitsi-meet,jitsi/lib-jitsi-meet,nevermind-corp/ljm,damencho/lib-jitsi-meet,dmurtari/lib-jitsi-meet,jitsi/lib-jitsi-meet,adambowles/lib-jitsi-meet,dmurtari/lib-jitsi-meet