Fixes that painting asset runtime that happens every time. (#56746)

Painting titles are not guaranteed to be unique, especially between categories.

code/modules/asset_cache/asset_list_items.dm

@@ -488,7 +488,8 @@
 		var/list/portrait = p
 		var/png = "data/paintings/[tab]/[portrait["md5"]].png"
 		if(fexists(png))
-			assets[portrait["title"]] = png
+			var/asset_name = "[tab]_[portrait["md5"]]"
+			assets[asset_name] = png
 	..() //this is where it registers all these assets we added to the list
 
 /datum/asset/simple/portraits/library