Item damage modification display fix

Fixes https://github.com/CleverRaven/Cataclysm-DDA/issues/4057

The bayonet was the only offender that modified weapon damage, but this should also fix any other modifications to an item in the future, including bashing damage. An example might be adding nails to any particular bashing item of your choice, giving it extra piercing damage, sharpening the blade of a sword, giving it extra cut damage, or adding a few weights for some bashing damage.