Fix bug were cards read before logging in cannot be read until a logout occurs

VendServer/VendServer.py

@@ -887,6 +887,7 @@ def handle_mifare_event(state, event, params, v, vstatus):
 			 (center('SORRY'), False, 0.5)])
 		vstatus.cur_user = ''
 		vstatus.cur_pin = ''
+		_last_card_id = -1
 	
 		reset_idler(v, vstatus, 2)
 		return