Prevent adding invalid values in CFFDict_setByKey (bug 1068432)

In the font in question, there are a couple of `topDict` entries that have invalid values (`0xF 0xF`, i.e. just eof markers without any actual numbers).
This causes the `parseFloatOperand` function, inside `CFFParser_parseDict`, to return `NaN`. Currently we pass this broken font onto the browser, which OTS unsurprisingly rejects.

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1068432.

test/pdfs/.gitignore

@@ -35,6 +35,7 @@
 !bug1020858.pdf
 !bug1050040.pdf
 !bug1200096.pdf
+!bug1068432.pdf
 !issue5564_reduced.pdf
 !canvas.pdf
 !bug1132849.pdf

test/test_manifest.json

@@ -203,6 +203,13 @@
        "lastPage": 1,
        "type": "eq"
     },
+    {  "id": "bug1068432",
+       "file": "pdfs/bug1068432.pdf",
+       "md5": "b76ac8d7d0ef471f28535c881f421e33",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue1512",
        "file": "pdfs/issue1512r.pdf",
        "md5": "af48ede2658d99cca423147085c6609b",

test/unit/cff_parser_spec.js

@@ -95,6 +95,15 @@ describe('CFFParser', function() {
     expect(topDict.getByName('Private')).toEqual([45, 102]);
   });
 
+  it('refuses to add topDict key with invalid value (bug 1068432)',
+      function () {
+    var topDict = cff.topDict;
+    var defaultValue = topDict.getByName('UnderlinePosition');
+
+    topDict.setByKey(/* [12, 3] = */ 3075, [NaN]);
+    expect(topDict.getByName('UnderlinePosition')).toEqual(defaultValue);
+  });
+
   it('parses a CharString having cntrmask', function() {
     var bytes = new Uint8Array([0, 1, // count
                                 1,  // offsetSize