DynamicsProcessor waveshaping fixed

[szeli1]

closes #1581

With this change the DynamicsProcessor plugin/effect will cause much less waveshaping.

This picture shows the difference in the output volume and the fft between the original (version 1.2.2) and the changed version. (keep in mind that the noise shown in the new version is because of clamping(?))

[szeli1]

test file: lmms_dynamics_processor_test.mmpz.txt

[sakertooth]

Closing in favor of #7168 (apologies for having you go through all of that, but a more proper solution seems to have been found).