Don't return users twice in "Welcome" from global room.

src/app/spreed-webrtc-server/roomworker.go

@@ -207,12 +207,14 @@ func (r *roomWorker) GetUsers() []*DataSession {
 			}
 		}
 		r.mutex.RUnlock()
+		if r.id != r.manager.globalRoomID {
 			// Include connections to global room.
 			for _, ec := range r.manager.GlobalUsers() {
 				if !appender(ec) {
 					break
 				}
 			}
+		}
 
 		out <- sl
 	}