Make last_scan_res update easier for static analyzers

The check based on last_scan_res_used is sufficient for making sure that
last_scan_res is allocated. However, it is a bit too complex for static
analyzers to notice, so add an explicit check to avoid bogus reports.

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

wpa_supplicant/bss.c

@@ -674,7 +674,8 @@ void wpa_bss_update_scan_res(struct wpa_supplicant *wpa_s,
 		wpa_s->last_scan_res_size = siz;
 	}
 
-	wpa_s->last_scan_res[wpa_s->last_scan_res_used++] = bss;
+	if (wpa_s->last_scan_res)
+		wpa_s->last_scan_res[wpa_s->last_scan_res_used++] = bss;
 }