cookie: fix memory leak on oversized rejection

Regression brought by 2bc230de63

Detected by OSS-fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3513
Assisted-by: Max Dymond

Closes #1930

lib/cookie.c

@@ -438,7 +438,7 @@ Curl_cookie_add(struct Curl_easy *data,
           /* too long individual name or contents, or too long combination of
              name + contents. Chrome and Firefox support 4095 or 4096 bytes
              combo. */
-          free(co);
+          freecookie(co);
           infof(data, "oversized cookie dropped, name/val %d + %d bytes\n",
                 nlen, len);
           return NULL;