Inline the `isRef` checks in the various `XRef.fetch` related methods
Inline the `isRef` checks in the various `XRef.fetch` related methods

The relevant methods are usually not hot enough for these changes to have an easily measurable effect, however there's been a lot of other cases where similiar inlining has helped performance. (And these changes may help offset the changes made in the next patch.)

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