With these changes `0`, `NaN`, `null`, and `undefined` in the `total`-property all result in `percent === NaN` being reported by the callback, since previously e.g. `0` would result in `percent === 100` being reported unconditionally which doesn't make a lot of sense.
Also, remove the "indeterminate" loadingBar (in the viewer) if the `PDFDocumentLoadingTask` fails since there won't be any more data arriving and displaying the animation thus seems wrong.
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