Make better use of getPath().

If you check `paths.exists()` first, then there's no benefit to calling `getPath(id)`: it always just returns `paths.get(id)`. It's more effective to let `getPath()` perform all of its checks.

src/lime/utils/PackedAssetLibrary.hx

@@ -242,7 +242,8 @@ import flash.media.Sound;
 			else
 			{
 				var basePath = rootPath == null || rootPath == "" ?  "" : Path.addTrailingSlash(rootPath);
-				var libPath = paths.exists(id) ? getPath(id) : id;
+				var libPath = getPath(id);
+				if (libPath == null) libPath = id;
 
 				var path = Path.join([basePath, libPath]);
 				path = __cacheBreak(path);