Overwrite glyphs contour count if it's less than -1.

The test pdf has a contour count of -70, but OTS doesn't
like values less than -1.

Fixes issue #7562.

src/core/fonts.js

@@ -649,6 +649,11 @@ var Font = (function FontClosure() {
     return (b0 << 8) + b1;
   }
 
+  function writeSignedInt16(bytes, index, value) {
+    bytes[index + 1] = value;
+    bytes[index] = value >>> 8;
+  }
+
   function signedInt16(b0, b1) {
     var value = (b0 << 8) + b1;
     return value & (1 << 15) ? value - 0x10000 : value;
@@ -1577,8 +1582,11 @@ var Font = (function FontClosure() {
           return glyphProfile;
         }
         var glyf = source.subarray(sourceStart, sourceEnd);
-        var contoursCount = (glyf[0] << 8) | glyf[1];
-        if (contoursCount & 0x8000) {
+        var contoursCount = signedInt16(glyf[0], glyf[1]);
+        if (contoursCount < 0) {
+          // OTS doesn't like contour count to be less than -1.
+          contoursCount = -1;
+          writeSignedInt16(glyf, 0, contoursCount);
           // complex glyph, writing as is
           dest.set(glyf, destStart);
           glyphProfile.length = glyf.length;

test/pdfs/.gitignore

@@ -188,6 +188,7 @@
 !issue2840.pdf
 !issue4061.pdf
 !issue4668.pdf
+!PDFJS-7562-reduced.pdf
 !issue5039.pdf
 !issue5070.pdf
 !issue5238.pdf

test/test_manifest.json

@@ -419,6 +419,12 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "PDFJS-7562-reduced",
+       "file": "pdfs/PDFJS-7562-reduced.pdf",
+       "md5": "ddfb96fd492599fe54adbc685493ba3a",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue3694_reduced",
        "file": "pdfs/issue3694_reduced.pdf",
        "md5": "c1438c7bad12d70c4cd684f8ce04448f",