made Assets.exists check for ASTC over PNG for now

Author: KarimAkra

src/openfl/utils/Assets.hx

@@ -75,6 +75,10 @@ class Assets
 	public static function exists(id:String, type:AssetType = null):Bool
 	{
 		#if lime
+		if (id != null && StringTools.endsWith(id, 'png') && type == null || type == IMAGE)
+		{
+			if (LimeAssets.exists(id.substr(0, id.length - 3) + 'astc', BINARY)) return true;
+		}
 		return LimeAssets.exists(id, cast type);
 		#else
 		return false;