Fix 2 crashes

bag.lua

@@ -80,8 +80,8 @@ local function on_place(itemstack, player, pointed_thing)
 		end
 	end
 
-	if selected_item then
-		local pos = edit.pointed_thing_to_pos(pointed_thing)
+	local pos = edit.pointed_thing_to_pos(pointed_thing)
+	if selected_item and pos then
 		edit.place_item_like_player(player, {name = selected_item}, pos)
 	end
 end

replace.lua

@@ -226,11 +226,12 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 					local pos = vector.new(x, y, z)
 					local node = minetest.get_node(pos)
 					local old_name = node.name
-					node.name = item_string
 					if replace_source_nodes[old_name] then
 						if is_node then
+							node.name = name
 							minetest.swap_node(pos, node)
 						else
+							node.name = item_string
 							edit.place_item_like_player(player, node, pos)
 						end
 					end