Fall back to the |defaultEncoding| when no valid "post" table is found in TrueType fonts (bug 1050040)

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1050040.

With this patch the file is completely readable, but given that the font is broken enough to be rejected by OTS the rendering differs slightly from Adobe Reader.

*Note:* the PDF file is sufficiently broken that even Adobe Reader complains about the font, *and* also about another more general issue.

test/pdfs/.gitignore

@@ -12,6 +12,7 @@
 !arial_unicode_ab_cidfont.pdf
 !arial_unicode_en_cidfont.pdf
 !asciihexdecode.pdf
+!bug1050040.pdf
 !canvas.pdf
 !complex_ttf_font.pdf
 !extgstate.pdf

test/test_manifest.json

@@ -579,6 +579,13 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "bug1050040",
+       "file": "pdfs/bug1050040.pdf",
+       "md5": "9076b29bd157e2646b457f29a4472a07",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "hudsonsurvey",
        "file": "pdfs/hudsonsurvey.pdf",
        "md5": "bf0e6576a7b6c2fe7485bce1b78e006f",