Add a reduced test-case for issue 7406

The PDF file contains an image that we're allowed to use, since it's just the PDF.js logo.
The logo image was simply inverted (so that it requires a /Decode entry in the image dictionary that triggers the use of `jpg.js` instead of the browser), converted to JPEG, and finally edited by hand to change the order of the DQT/SOF{n} markers.

test/pdfs/.gitignore

@@ -30,6 +30,7 @@
 !issue7200.pdf
 !issue7229.pdf
 !issue7403.pdf
+!issue7406.pdf
 !issue7426.pdf
 !issue7439.pdf
 !issue7446.pdf

test/test_manifest.json

@@ -976,6 +976,13 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "issue7406",
+       "file": "pdfs/issue7406.pdf",
+       "md5": "7a3d322d7c595a36b4470cfb6a54a2b7",
+       "link": false,
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "protectip",
        "file": "pdfs/protectip.pdf",
        "md5": "676e7a7b8f96d04825361832b1838a93",