[Vanilla Bug] Fix crash when `InfantryClass::Take_Damage` is called with a null warhead

[Rampastring]

Description:

InfantryClass::Take_Damage does not check if the warhead parameter is null. In some cases it can be called with a null warhead, which leads to a crash.

Additional Files:

Fixed in CnCNet ts-patches: https://github.com/CnCNet/ts-patches/blob/master/src/mods/fix_infantryclass_take_damage_null_warhead_crash.asm