Do not deregister Strophe listener on missing room, fix removeCommandListener

JitsiConference.js

 /**
   * Removes command  listener
   * @param command {String} the name of the command
+  * @param handler {Function} handler to remove for the command
   */
-JitsiConference.prototype.removeCommandListener = function(command) {
+JitsiConference.prototype.removeCommandListener = function(command, handler) {
     if (this.room) {
-        this.room.removePresenceListener(command);
+        this.room.removePresenceListener(command, handler);
     }
 };
 

modules/xmpp/strophe.emuc.js

         const room = this.rooms[Strophe.getBareJidFromJid(from)];
 
         if (!room) {
-            return;
+            return true;
         }
 
         // Parse status.
         const room = this.rooms[Strophe.getBareJidFromJid(from)];
 
         if (!room) {
-            return;
+            return true;
         }
 
         room.onPresenceUnavailable(pres, from);
         const room = this.rooms[Strophe.getBareJidFromJid(from)];
 
         if (!room) {
-            return;
+            return true;
         }
 
         room.onPresenceError(pres, from);
         const room = this.rooms[Strophe.getBareJidFromJid(from)];
 
         if (!room) {
-            return;
+            return true;
         }
 
         room.onMessage(msg, from);
         const from = iq.getAttribute('from');
         const room = this.rooms[Strophe.getBareJidFromJid(from)];
 
-        // XXX What are the semantics of the return value? Why is it sometimes
-        // undefined and sometimes a boolean?
+        // Returning false would result in the listener being deregistered by Strophe
         if (!room) {
-            return;
+            return true;
         }
 
         room.onMute(iq);