* 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)