diff osc/sv-command @ 149:37cb005f7c40

* FFT: fix invalid write of normalisation factor in compact mode of disc cache
* FFT: fix range problem for normalisation factor in compact mode (it was
  stored as an unsigned scaled from an assumed float range of 0->1, which
  is not very plausible and not accurate enough even if true -- use a float
  instead)
* Spectrogram: fix vertical zoom behaviour for log frequency spectrograms:
  make the thing in the middle of the display remain in the middle after zoom
* Overview widget: don't update the detailed waveform if still decoding the
  audio file (too expensive to do all those redraws)