Check if `pageView.pdfPage` exists in `PDFViewer._ensurePdfPageLoaded`, to avoid potentially calling `PDFPageView.setPdfPage` multiple times for the same page
Check if `pageView.pdfPage` exists in `PDFViewer._ensurePdfPageLoaded`, to avoid potentially calling `PDFPageView.setPdfPage` multiple times for the same page

Since calling `PDFPageView.setPdfPage` will in turn call `PDFPageView.reset`, which cancels all rendering and completely resets the page, it's thus possible that we currently cause some unnecessary re-rendering during the initial loading phase of the viewer.

Depending on the order in which data arrives, it's possible (and in practice always seem to happen) that the `pdfPage` property of the *second* page has already been set during `PDFViewer.setDocument`, by the time that the request for the `pdfPage` is resolved in `PDFViewer._ensurePdfPageLoaded`.

Also, note how the `setPdfPage` call in `PDFViewer.setDocument` is already guarded by this kind of check.

websirnik/pdf.js,Rob--W/pdf.js,Shoobx/pdf.js,skalnik/pdf.js,mozilla/pdf.js,macroplant/pdf.js,Snuffleupagus/pdf.js,caremerge/pdf.js,mainegreen/pdf.js,macroplant/pdf.js,mozilla/pdf.js,Rob--W/pdf.js,mukulmishra18/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,caremerge/pdf.js,showpad/mozilla-pdf.js,skalnik/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,xavier114fch/pdf.js,Snuffleupagus/pdf.js,ydfzgyj/pdf.js,tinderboxhq/pdf.js,ydfzgyj/pdf.js,tinderboxhq/pdf.js,mozilla/pdf.js,mukulmishra18/pdf.js,1and1/pdf.js,adlerweb/pdf.js-Touch,nawawi/pdf.js,nawawi/pdf.js,Shoobx/pdf.js,mainegreen/pdf.js,showpad/mozilla-pdf.js,xavier114fch/pdf.js,timvandermeij/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,timvandermeij/pdf.js,1and1/pdf.js,adlerweb/pdf.js-Touch,websirnik/pdf.js