http: fix superfluous null line in range request header

At least the apache sever is very unhappy with that extra null line and will
take more than ten seconds in responding to each range request, which slows
down a lot the entire http file transfer process or even time out.

grub-core/net/http.c

@@ -381,9 +381,8 @@ http_establish (struct grub_file *file, grub_off_t offset, int initial)
       ptr = nb->tail;
       grub_snprintf ((char *) ptr,
 		     sizeof ("Range: bytes=XXXXXXXXXXXXXXXXXXXX-"
-			     "\r\n"
 			     "\r\n"),
-		     "Range: bytes=%" PRIuGRUB_UINT64_T "-\r\n\r\n",
+		     "Range: bytes=%" PRIuGRUB_UINT64_T "-\r\n",
 		     offset);
       grub_netbuff_put (nb, grub_strlen ((char *) ptr));
     }