Further ensure that `PDFFindController._requestMatchesCount` won't return broken data (PR 10052 follow-up)
Further ensure that `PDFFindController._requestMatchesCount` won't return broken data (PR 10052 follow-up)

This prevents the findbar from intermittently displaying `0 of {number} matches`, which *could* theoretically happen for large and/or slow loading documents.

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