Fix one case of phantom viewers

www/common/outer/onlyoffice.js

@@ -205,12 +205,14 @@ define([
             }
         }
 
+        if (ctx.clients[clientId]) {
             var oldChannel = ctx.clients[clientId].channel;
             var oldChan = ctx.channels[oldChannel];
             if (oldChan) {
                 ctx.emit('LEAVE', {id: clientId}, [oldChan.clients[0]]);
             }
             delete ctx.clients[clientId];
+        }
     };