Fix a xfaFaxtory typo in the shadowing in the PDFDocument.xfaFactory getter

With this typo the shadowing doesn't actually work, which causes these checks to be unnecessarily repeated. In this particular case it didn't have a significant performance impact, however we should definately fix this nonetheless.

src/core/document.js

@@ -892,7 +892,7 @@ class PDFDocument {
       const data = this.xfaData;
       return shadow(this, "xfaFactory", data ? new XFAFactory(data) : null);
     }
-    return shadow(this, "xfaFaxtory", null);
+    return shadow(this, "xfaFactory", null);
   }
 
   get isPureXfa() {