perf: Stop parsing the mp4 when the init segment is encrypted on ContentWorkarounds (#8353)

Author: avelad

lib/media/content_workarounds.js

@@ -50,6 +50,7 @@ shaka.media.ContentWorkarounds = class {
 
     const onEncryptionMetadataBox = (box) => {
       isEncrypted = true;
+      box.parser.stop();
     };
 
     // Multiplexed content could have multiple boxes that we need to modify.