MINOR: stats: send content-length with the redirect to allow keep-alive

After a POST on the stats admin page, a 303 is emitted. Unfortunately
this 303 doesn't contain a content-length, which forces the connection
to be closed and reopened. Let's simply add a content-length: 0 to solve
this.
(cherry picked from commit fdfcc9d2b75e97f81b40f80ddd341ab77550f43b)
(cherry picked from commit 893e5405762944627176f50ee101a33a35d2fbeb)
1 file changed