Normal weapon resistance is applied twice for NPCs

A very long term regression of PR 2068 noticed by @madsbuvi in !4334 (merged); normal weapon resistance is applied to the damage again if an NPC is hit as the original code wasn't properly removed. It was implemented correctly for creatures and it can't result in a duplicate messagebox (i.e. a resistance of 50% halves the damage twice, a resistance of 100% doesn't trigger the second call) which is probably why it hasn't ever been noticed.