fix double controller on Coursera

inject.js

@@ -218,7 +218,15 @@ chrome.extension.sendMessage({}, function(response) {
       function checkForVideo(node, parent, added) {
         if (node.nodeName === 'VIDEO') {
           if (added) {
-            if (!node.classList.contains('vsc-initialized')) {
+            if (!node.classList.contains('vsc-initialized') && !node.dataset['vscid']) {
+              new tc.videoController(node, parent);
+            }
+            // if the video has already been initialized, then it has been mutated
+            // we may need to update the controller location to reflect this
+            else {
+              let id = node.dataset['vscid'];
+              let ctrl = document.querySelector(`div[data-vscid="${id}"]`);
+              if (ctrl) ctrl.remove();
               new tc.videoController(node, parent);
             }
           } else {