Adjust the heuristics used to detect OpenType font file with CFF data (bug 1186827, bug 1182130, issue 6264)

*This is a tentative patch.*

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1186827.
Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1182130.
Fixes 6264.

test/pdfs/.gitignore

@@ -132,6 +132,8 @@
 !issue4800.pdf
 !issue4801.pdf
 !issue5334.pdf
+!bug1186827.pdf
+!issue215.pdf
 !issue5540.pdf
 !issue5549.pdf
 !issue5475.pdf

test/test_manifest.json

@@ -435,6 +435,20 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "bug1186827",
+       "file": "pdfs/bug1186827.pdf",
+       "md5": "6c5526ae1a9d66cb517153001afc196e",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
+    {  "id": "issue215",
+       "file": "pdfs/issue215.pdf",
+       "md5": "31f3dc60ecf008987d970edfd2b1df61",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "bug850854",
        "file": "pdfs/bug850854.pdf",
        "md5": "346a034a80120d123b9fefc42bcb11da",