bruteF04C3

Results 5 issues of bruteF04C3

undefined and "not defined" are two different things, updated for the sake of clarity

I have installed this inside a project running on angular v12. Getting the following error while running / serving the app ![image](https://github.com/intbot/ng2-pdfjs-viewer/assets/71308081/334c0995-5232-4594-a542-e5501604c553)

The "refresh" button can be clearly seen overlapping the "add" button in the respective list. Hence this fix