browser cbt runtime fix

code/datums/browser.dm

@@ -43,8 +43,10 @@
 		var/datum/asset/spritesheet/sheet = name
 		stylesheets["spritesheet_[sheet.name].css"] = "data/spritesheets/[sheet.name]"
 	else
-		stylesheets["[ckey(name)].css"] = file
-		register_asset("[ckey(name)].css", file)
+		var/asset_name = "[name].css"
+		stylesheets[asset_name] = file
+		if(!SSassets.cache[asset_name])
+			register_asset(asset_name, file)
 
 /datum/browser/proc/set_content(ncontent)
 	content = ncontent