skip cross references outside file

if the previous cross-reference location points to an offset outside the file size we skip it.

also makes cid font factory more resilient by skipping missing descriptors.

src/UglyToad.PdfPig/Parser/FileStructure/CrossReferenceParser.cs

@@ -52,6 +52,11 @@
             {
                 log.Debug($"Reading cross reference table or stream at {previousCrossReferenceLocation}.");
 
+                if (previousCrossReferenceLocation >= bytes.Length)
+                {
+                    break;
+                }
+
                 // seek to xref table
                 tokenScanner.Seek(previousCrossReferenceLocation);
 

src/UglyToad.PdfPig/PdfFonts/Parser/Parts/CidFontFactory.cs

@@ -84,9 +84,16 @@
                 return false;
             }
 
-            var descriptor = DirectObjectFinder.Get<DictionaryToken>(baseValue, pdfScanner);
+            try
+            {
+                var descriptor = DirectObjectFinder.Get<DictionaryToken>(baseValue, pdfScanner);
 
-            descriptorDictionary = descriptor;
+                descriptorDictionary = descriptor;
+            }
+            catch
+            {
+                return false;
+            }
 
             return true;
         }