http_static: fix memory hss_session using after be freed

Type: fix

Change-Id: Ic3d3de4198310361de876a8224e4f7cd0b48b698
Signed-off-by: XiaomingJiang <jiangxiaoming@outlook.com>
diff --git a/src/plugins/http_static/static_server.c b/src/plugins/http_static/static_server.c
index 9d9a68f..48e71f5 100644
--- a/src/plugins/http_static/static_server.c
+++ b/src/plugins/http_static/static_server.c
@@ -58,8 +58,6 @@
 {
   hss_main_t *hsm = &hss_main;
 
-  pool_put (hsm->sessions[hs->thread_index], hs);
-
   if (CLIB_DEBUG)
     {
       u32 save_thread_index;
@@ -68,6 +66,8 @@
       memset (hs, 0xfa, sizeof (*hs));
       hs->thread_index = save_thread_index;
     }
+
+  pool_put (hsm->sessions[hs->thread_index], hs);
 }
 
 /** \brief Disconnect a session