Fix usage of #write_string in OptCarrot

* The data and buffer are exactly 4096 bytes, there is no space for an extra byte.

Author: eregon

bench/optcarrot/lib/optcarrot/driver/misc.rb

@@ -105,7 +105,7 @@ def icon_data
       end
       dat = dat.bytes.map {|clr| palette[clr - 35] }
 
-      return width, height, pixels.write_string(dat.pack("V*"))
+      return width, height, pixels.write_bytes(dat.pack("V*"))
     end
   end
 end