Tweak the `PDFHistory._tryPushCurrentPosition` method to work better with the different Scroll/Spread viewer modes
Tweak the `PDFHistory._tryPushCurrentPosition` method to work better with the different Scroll/Spread viewer modes

Given that a larger number of pages may now be visible at once, and importantly that their layout may be non-vertical, one of the conditions should be tweaked to not accidentally miss cases where a page is still visible.

Please note: This patch is based on code-inspection, and the only ill effect occurring without it would be a couple of (near) duplicate history entries in some *rare* edge-cases.

caremerge/pdf.js,mozilla/pdf.js,Snuffleupagus/pdf.js,macroplant/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,macroplant/pdf.js,mainegreen/pdf.js,caremerge/pdf.js,mukulmishra18/pdf.js,xavier114fch/pdf.js,mukulmishra18/pdf.js,Snuffleupagus/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,Shoobx/pdf.js,mozilla/pdf.js,timvandermeij/pdf.js,nawawi/pdf.js,macroplant/pdf.js,xavier114fch/pdf.js,mozilla/pdf.js,mainegreen/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,Shoobx/pdf.js,showpad/mozilla-pdf.js