Use optional chaining in `web/pdf_history.js`
Use optional chaining in `web/pdf_history.js`

Since we're now free to use e.g. optional chaining everywhere *except* for the worker, we can thus simplify this code a bit.

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