P2P: Allow p2p_get_group_num_members() to be called with NULL

This make it easier to use wpa_s->p2p_group without having to check
whether there is a group initialized on this wpa_s instance.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/p2p/p2p_group.c

@@ -981,6 +981,9 @@ u8 p2p_group_presence_req(struct p2p_group *group,
 
 unsigned int p2p_get_group_num_members(struct p2p_group *group)
 {
+	if (!group)
+		return 0;
+
 	return group->num_members;
 }