Fix potential null issue

src/utils.ts

@@ -343,6 +343,7 @@ export default class Utils {
             //for embeds
             const player = document.getElementById("player");
             referenceNode = player.firstChild as HTMLElement;
+            if (referenceNode) {
                 let index = 1;
 
                 //find the child that is the video player (sometimes it is not the first)
@@ -352,6 +353,7 @@ export default class Utils {
                     index++;
                 }
             }
+        }
 
         return referenceNode;
     }