Prevent `readCmapTable` from failing if the `cmap` is missing in TrueType fonts

Fixes http://arrow.dit.ie/cgi/viewcontent.cgi?article=1000&context=aaschadpoth#page=3.

src/core/fonts.js

@@ -3226,6 +3226,15 @@ var Font = (function FontClosure() {
        * PDF spec
        */
       function readCmapTable(cmap, font, isSymbolicFont, hasEncoding) {
+        if (!cmap) {
+          warn('No cmap table available.');
+          return {
+            platformId: -1,
+            encodingId: -1,
+            mappings: [],
+            hasShortCmap: false
+          };
+        }
         var segment;
         var start = (font.start ? font.start : 0) + cmap.offset;
         font.pos = start;

test/pdfs/.gitignore

@@ -2,6 +2,7 @@
 *.error
 
 !tracemonkey.pdf
+!TrueType_without_cmap.pdf
 !franz.pdf
 !franz_2.pdf
 !xref_command_missing.pdf

test/test_manifest.json

@@ -1196,6 +1196,13 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "TrueType_without_cmap",
+       "file": "pdfs/TrueType_without_cmap.pdf",
+       "md5": "afca8bb11f2e1f7298b4e5dd85785fb0",
+       "link": false,
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue3323",
        "file": "pdfs/issue3323.pdf",
        "md5": "1a14ff574013caeafa9d598269988764",