make Curl_cookie_clearall() survive getting called with a NULL pointer

lib/cookie.c

diff --git a/lib/cookie.c b/lib/cookie.c
index 0cd79d3..2856ad8 100644
--- a/lib/cookie.c
+++ b/lib/cookie.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2006, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2007, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -806,9 +806,11 @@
  ****************************************************************************/
 void Curl_cookie_clearall(struct CookieInfo *cookies)
 {
-  Curl_cookie_freelist(cookies->cookies);
-  cookies->cookies = NULL;
-  cookies->numcookies = 0;
+  if(cookies) {
+    Curl_cookie_freelist(cookies->cookies);
+    cookies->cookies = NULL;
+    cookies->numcookies = 0;
+  }
 }
 
 /*****************************************************************************