Update DefaultProjectileWeapon.lua

Switched to different is destroyed check
did basis test with T3 arti in sandbox and seemed to work (but the replay didn't have an error arising in the first place more a test that it's not broken something)

lua/sim/weapons/DefaultProjectileWeapon.lua

@@ -411,7 +411,7 @@ DefaultProjectileWeapon = ClassWeapon(Weapon) {
     ---@param self DefaultProjectileWeapon
     EconomyDrainThread = function(self)
         WaitFor(self.EconDrain)
-        if self.unit.BeenDestroyed and not(self.unit:BeenDestroyed()) then
+        if self.unit and not(IsDestroyed(self.unit)) then
             RemoveEconomyEvent(self.unit, self.EconDrain)
         end
         self.EconDrain = nil