[Firefox] Handle errors if loading failed before the "supportsRangedLoading" message was sent (bug 1732141)
[Firefox] Handle errors if loading failed before the "supportsRangedLoading" message was sent (bug 1732141)

This is a follow-up to PR 10675, since there I completely overlooked that we also need to handle the case where a PDF document has *failed* to load when the "supportsRangedLoading" message is sent to the viewer.

macroplant/pdf.js,timvandermeij/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,Shoobx/pdf.js,nawawi/pdf.js,mozilla/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,Shoobx/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,macroplant/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,Snuffleupagus/pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js