Handle missing encoding differences array

pdf.js

@@ -4324,14 +4324,16 @@ var PartialEvaluator = (function() {
             baseEncoding = Encodings[baseName.name].slice();
 
           // Load the differences between the base and original
-          var diffEncoding = encoding.get('Differences');
-          var index = 0;
-          for (var j = 0; j < diffEncoding.length; j++) {
-            var data = diffEncoding[j];
-            if (IsNum(data))
-              index = data;
-            else
-              differences[index++] = data.name;
+          if (encoding.has('Differences')) {
+            var diffEncoding = encoding.get('Differences');
+            var index = 0;
+            for (var j = 0; j < diffEncoding.length; j++) {
+              var data = diffEncoding[j];
+              if (IsNum(data))
+                index = data;
+              else
+                differences[index++] = data.name;
+            }
           }
         } else if (IsName(encoding)) {
           baseEncoding = Encodings[encoding.name].slice();

test/pdfs/txt2pdf.pdf.link

@@ -0,0 +1 @@
+http://www.sanface.com/pdf/test.pdf

test/test_manifest.json

@@ -133,5 +133,11 @@
        "link": true,
        "rounds": 1,
        "type": "load"
+    },
+    {  "id": "txt2pdf",
+       "file": "pdfs/txt2pdf.pdf",
+       "link": true,
+       "rounds": 1,
+       "type": "load"
     }
 ]