Check if hitter has inventory when punching item

Fixes #3280

builtin/game/item_entity.lua

@@ -200,9 +200,10 @@ core.register_entity(":__builtin:item", {
 	end,
 
 	on_punch = function(self, hitter)
-		if self.itemstring ~= '' then
-			local left = hitter:get_inventory():add_item("main", self.itemstring)
-			if not left:is_empty() then
+		local inv = hitter:get_inventory()
+		if inv and self.itemstring ~= '' then
+			local left = inv:add_item("main", self.itemstring)
+			if left and not left:is_empty() then
 				self.itemstring = left:to_string()
 				return
 			end