Fix Pefect-FLAC-Encode.log logging for hidden tracks:
- The code had assumed that the hidden track is called "00 - pregap.wav" but it is actually called "Track 00.wav" nowadays. This was caused by commit 4fa2289e7bca51894e926ea46e3290a797f20d5f which changed the filename format of the WAV singletracks.
- Fortunately, the bug caused no damage to the audio data. The only effect is that the log file says that there was no hidden track even though there was one.