defensive_assert!
* Add defensive_assert macro Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Apply review suggestions Co-authored-by: Bastian Köcher <git@kchr.de> Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> --------- Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>