Fixed channel parsing error.

Fixes whitelisting issues.

content.js

@@ -499,10 +499,14 @@ function updatePreviewBar() {
 function getChannelID() {
     //get channel id
     let channelNameContainer = document.getElementById("channel-name");
+
+    if (channelNameContainer === null) {
+        //try later
+        return false;
+    }
+
     let channelURLContainer = channelNameContainer.querySelector("#container").querySelector("#text-container").querySelector("#text").firstElementChild;
 
-
-
     if (channelURLContainer === null) {
         //old YouTube theme
         let channelContainers = document.getElementsByClassName("yt-user-info");