hostapd: Check that EVENT_ASSOC data is present before using it

While hostapd should not really receive the EVENT_ASSOC message for
IBSS, driver_nl80211.c could potentially generate that if something
external forces the interface into IBSS mode and the IBSS case does not
provide the struct assoc_info data. Avoid the potential NULL pointer
dereference by explicitly verifying for the event data to be present.

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

src/ap/drv_callbacks.c

@@ -1044,6 +1044,8 @@ void wpa_supplicant_event(void *ctx, enum wpa_event_type event,
 				       data->eapol_rx.data_len);
 		break;
 	case EVENT_ASSOC:
+		if (!data)
+			return;
 		hostapd_notif_assoc(hapd, data->assoc_info.addr,
 				    data->assoc_info.req_ies,
 				    data->assoc_info.req_ies_len,