1.44 - Fix YT Center compatibility - Fix #7

* Fix a second video player getting loaded when running this script along Youtube Center, this reintroduces the progressbar bug for users with YT Center. Please use the [dev build of YT Center](https://github.com/YePpHa/YouTubeCenter/raw/master/dist/YouTubeCenter.user.js) until the author pushes the fix to the main build.