High Quality Pitch Scaler + Hard Limiter results in artefact

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D.Ipsum reports this on forum:

> 1) open LMMS
> 2) add a Hard Limiter on the master
> 3) add 2 Vibed in the Song Editor
> 4) put some notes in the Piano-Roll so that both Vibed play at the same time
> 5) add a High Quality Pitch Scaler in the FX tab of both Vibed
>
> > When two instances of High Quality Pitch Scaler play at the same time, it generates a horrible noise (it's the same with TripleOsc ... I did not try on other synths)
>
> 6) Disable one of the two High Quality Pitch Scaler
>
> > When both Vibed play at the same time (so with only one High Quality Pitch Scaler), everything is fine.

Here with 3oc:
[issue_HardLimiterPitchScaler.txt](https://github.com/LMMS/lmms/files/1595887/issue_HardLimiterPitchScaler.txt)

Start with the reproduction steps in the issue and inspect issue_HardLimiterPitchScaler.txt. Reproduce the artifact with two High Quality Pitch Scaler instances and the Hard Limiter, then compare it with one instance and the TripleOsc case. Done means the reported horrible noise no longer occurs in these combinations.

Written by the indexing model from the issue text.