bug: crash when resizing cancelled spectrogram window

[kgorham]

To reproduce:

1. Open clip 'Lahu Shi 1-3.wav'
2. Select layout with waveform/spectrogram
3. Enable the formant track rendering via the toolbar.
4. Wait a couple seconds and cancel the rendering by pressing escape.
5. Grab the lower right corner of the spectrogram window and continually resize the window. After a while it will crash.

Code fails due to access violation.

Line:
*pPixel = (uint8)((pPowerLeft[y] * nLeft + pPowerRight[y] * nRight + 8192) >> 14);

Call stack:

SA.exe!CPlotSpectrogram::OnDrawSpectrogram(CDC * pDC, CRect rWnd, CRect rClip, CSaView * pView, int bSmooth, int * bAliased) Line 606 C++
SA.exe!CPlotSpectrogram::OnDraw2(CDC * pDC, CRect rWnd, CRect rClip, CSaView * pView) Line 1032 C++
SA.exe!CPlotSpectrogram::OnDraw(CDC * pDC, CRect rWnd, CRect rClip, CSaView * pView) Line 1130 C++
SA.exe!CPlotWnd::OnPaint() Line 2035 C++
[External Code]
mfc140ud.dll![Frames below may be incorrect and/or missing, no symbols loaded for mfc140ud.dll] Unknown
SA.exe!wWinMain(HINSTANCE__ * hInstance, HINSTANCE__ * hPrevInstance, wchar_t * lpCmdLine, int nCmdShow) Line 26 C++