spectrogram: Infinite loop in calculate_ticks if step == 0

[coypoop]

A file generating this infinite loop is available here: http://coypu.sdf.org/dial1.audio
(Also unclear why the spectrogram is the way it is for this file).

[janstary]

To confirm, sndfile-spectrogram dial1.audio 640 480 file.png
never finishes, eats up the CPU, and does not produce a file.
This is on OpenBSD 7.5/amd64.

[janstary]

@coypoop : How did you even get the spectrogram, if it never finishes?

[coypoop]

I don't remember, I might have edited the code to avoid the infinite loop.