Fix corruption crash when zooming on a large sample

[khoidauminh]

Fixes #7576

Bug is very weird, so is PR.

I'd like to hear if there is a more solid fix.

[sakertooth]

Doesn't even crash in debug mode...

[khoidauminh]

@sakertooth When compiled with Release or ReleaseWithInfo I see crashes when the vectors de-allocate. I still see those vectors are unnecessary and add both overhead and memory cost.

Should we remove them, or should we wait til the sample cache/database PR gets merged and switch to the thumbnails at once?

[sakertooth]

I'm going to submit a PR that basically starts the implementation of SampleWaveform::visualize at a clean slate. I've tried to make it as simple as possible and not worry about optimizations, considering the work me and you are doing with sample thumbnails. It removes all the vector allocations and only uses a single loop.