fix(transcode): fix duplicate transcode path for extra files

[enncoded]

Fixes duplicate destination path for extra files (cover images, txt files).

For example: If the image file in the original content directory is ./content/various artists - songs for the amazon vol. 1/cover.png (and the transcode directory is ./transcoded), transcode_folder_path becomes ./transcoded/Various Artists - songs for the amazon vol. 1 [2020] (WEB - FLAC)/./transcoded/Various Artists - songs for the amazon vol. 1 [2020] (WEB - FLAC) because output_dir and folder_path are the same.

Therefore, the destination path for the cover image ends up as ./transcoded/Various Artists - songs for the amazon vol. 1 [2020] (WEB - FLAC)/./transcoded/Various Artists - songs for the amazon vol. 1 [2020] (WEB - FLAC)/cover.png/cover.png, when it should be ./transcoded/Various Artists - songs for the amazon vol. 1 [2020] (WEB - FLAC)/cover.png