MINOR: startup: don't rely on PR_STNEW to check for listeners

Instead of looking at listeners in proxies in PR_STNEW state, we'd
rather check for listeners in those not in PR_STSTOPPED as it's only
this state which indicates the proxy was disabled. And let's check
the listeners count instead of testing the list's head.

src/haproxy.c

@@ -2010,7 +2010,7 @@ static void init(int argc, char **argv)
 				break;
 
 		for (px = proxies_list; px; px = px->next)
-			if (px->state == PR_STNEW && !LIST_ISEMPTY(&px->conf.listeners))
+			if (px->state != PR_STSTOPPED && px->li_all)
 				break;
 
 		if (pr || px) {