[Test] Mark "connection" resource as freed

mt.disconnect() performs free(). If we call it twice with the same argument, we will get double free()

1 files changed, 4 insertions, 1 deletions

diff --git a/test/functional/lua/miltertest/lib.lua b/test/functional/lua/miltertest/lib.lua
index f7dc3cc79..e94efd559 100644
--- a/test/functional/lua/miltertest/lib.lua
+++ b/test/functional/lua/miltertest/lib.lua
@@ -21,7 +21,10 @@ function setup(c_ip, helo, hn)
 end
 
 function teardown()
-  mt.disconnect(conn)
+  if conn then
+    mt.disconnect(conn)
+  end
+  conn = nil
 end
 
 function send_message(body, hdrs, id, sender, rcpts)