In Tooltip_AddWorldDrop(): Check to see if there is a valid item_id before calling GetItemInfo()

diff --git a/Frame.lua b/Frame.lua
index 9c2e802..964263e 100644
--- a/Frame.lua
+++ b/Frame.lua
@@ -728,7 +728,12 @@ do
 		if location and drop_location ~= location then
 			return
 		end
-		local _, _, _, item_level = GetItemInfo(private.spell_to_recipe_map[recipe_id])
+		local item_id = private.spell_to_recipe_map[recipe_id]
+		local _, item_level
+
+		if item_id then
+			_, _, _, item_level = GetItemInfo(item_id)
+		end
 		local type_color = string.gsub(quality_color, "|cff", "")

 		if type(id_num) == "string" then