Fix client error on selecting server with no channels

web/static/js/main.js

@@ -62,7 +62,7 @@ function update_select(sel) {
         channelDisplay.textContent = `#${sel.selectedOptions[0].textContent}`;
     }
 
-    if (sel.selectedOptions[0] === null) {
+    if (sel.selectedOptions[0] === undefined) {
         return;
     }