Correctly detect OpenType font files with CFF data

Fixes 5334.
Fixes 215.
Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1125614.

According to the specification, http://www.microsoft.com/typography/otspec/otff.htm, OpenType font files with CFF data should have `OTTO` in the header.

test/pdfs/.gitignore

@@ -113,6 +113,7 @@
 !issue4722.pdf
 !issue4800.pdf
 !issue4801.pdf
+!issue5334.pdf
 !issue5549.pdf
 !issue5475.pdf
 !issue5481.pdf

test/test_manifest.json

@@ -421,6 +421,13 @@
        "rounds": 1,
        "type": "load"
     },
+    {  "id": "issue5334",
+       "file": "pdfs/issue5334.pdf",
+       "md5": "5575020f37f6e5b3c43b8183bf7f96ae",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "bug850854",
        "file": "pdfs/bug850854.pdf",
        "md5": "346a034a80120d123b9fefc42bcb11da",