Log Message:
audio/fasttracker2: Updates to v1.38

Changes since v1.36

v1.38 - 01.11.2020
- Fixed two possible pattern length bugs while switching to a new, shorter
  pattern while the song is playing.
- Mixer code cleanup (generates smaller code now)

v1.37 - 29.10.2020
- The 4-tap cubic spline resampling interpolation has now been replaced with
  8-tap windowed-sinc (polyphase) for better audio quality.
- The mixer is now using 64-bit float precision instead of 32-bit float
  precision. We only mix up to 32 channels anyway, which is not very CPU
  intensive.
- Volume/panning envelope interpolation is now using floating point precision
  instead of 8.8 fixed-point precision.
- Fixed a bug where the scopes would not shut down if you triggered an
  instrument that is not allocated (empty).
- Small code cleanup