[type1] Fix heap buffer overflow.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=36

* src/type1/t1load.c (parse_charstrings): Reject fonts that don't
contain glyph names.

ChangeLog

@@ -1,3 +1,14 @@
+2016-08-26  Werner Lemberg  <wl@gnu.org>
+
+	[type1] Fix heap buffer overflow.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=36
+
+	* src/type1/t1load.c (parse_charstrings): Reject fonts that don't
+	contain glyph names.
+
 2016-08-25  Werner Lemberg  <wl@gnu.org>
 
 	[sfnt] Fix previous commit (#48901).

src/type1/t1load.c

@@ -1776,6 +1776,12 @@
       }
     }
 
+    if ( !n )
+    {
+      error = FT_THROW( Invalid_File_Format );
+      goto Fail;
+    }
+
     loader->num_glyphs = n;
 
     /* if /.notdef is found but does not occupy index 0, do our magic. */