r1473 merge:

decrement active connection counter in mail proxy

src/mail/ngx_mail_handler.c

@@ -2100,6 +2100,10 @@ ngx_mail_close_connection(ngx_connection_t *c)
 
 #endif
 
+#if (NGX_STAT_STUB)
+    ngx_atomic_fetch_add(ngx_stat_active, -1);
+#endif
+
     c->destroyed = 1;
 
     pool = c->pool;