blank page detection in reader mode

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Just an idea to make reader mode a bit more friendly:

When using reader mode with a PDF that has large margins at the bottom, a page will turn that is essentially blank. A simple (!) way around this would be to compute the next page and see if there is any non-whitespace in the region that was just revealed. If so, show it; if not, skip to the next page. It wouldn't be enough to just detect all-blank pages, as sometimes the overlap from the previous page is all that displays.