BUG/MEDIUM: check: tcpcheck regression introduced by e16c1b3f

The commit e16c1b3f changed the way the function tcpcheck_get_step_id is
now called (check instead of server).
This change introduced a regression since now this function would return
0 all the time because of:
 if (check->current_step)
   return 0;

This patch fixes this issue by inversing the test: you want to return 0
only if current_step is not yet set :)

No backport is needed.
diff --git a/src/checks.c b/src/checks.c
index 3702d9a..8a0231d 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -2363,7 +2363,7 @@
 	int i = 0;
 
 	/* not even started anything yet => step 0 = initial connect */
-	if (check->current_step)
+	if (!check->current_step)
 		return 0;
 
 	cur = check->last_started_step;