Don't map glyphs to Unicode "Dotted circle" combining mark (bug 1108301)

It seems that `0x25CC` is another bad spot for charCodes.
Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1108301.

test/pdfs/.gitignore

@@ -30,6 +30,7 @@
 !bug847420.pdf
 !bug860632.pdf
 !bug894572.pdf
+!bug1108301.pdf
 !pdfjsbad1586.pdf
 !freeculture.pdf
 !pdfkit_compressed.pdf

test/test_manifest.json

@@ -1113,6 +1113,13 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "bug1108301",
+       "file": "pdfs/bug1108301.pdf",
+       "md5": "cc94cc7e5f5e281dfa7e21020dd90cc7",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue1466",
       "file": "pdfs/issue1466.pdf",
       "md5": "8a8877432e5bb10cfd50d60488d947bb",