items/mcl_banners: expand confusing conditional append

https://git.minetest.land/Mineclonia/Mineclonia/pulls/15/files#issuecomment-22785

mods/ITEMS/mcl_banners/init.lua

@@ -164,7 +164,11 @@ local make_banner_overlay = function(base_color, layers)
 			-- Generate layer texture
 			local layer = "((("..pattern.."^[mask:mcl_banners_front.png)^[colorize:"..color..":"..layer_ratio..")^[mask:"..pattern..")"
 
-			lovl = (lovl ~= "" and (lovl .. "^") or "") .. layer
+			if lovl ~= "" then
+				lovl=lovl.."^"..layer
+			else
+				lovl=layer
+			end
 		end
 
 		return "[combine:32x32:0,0=" .. escape(base) .. ":7,3=" .. escape("("..lovl.."^[resize:50x38)")