Amend changelog: previous MED fixes for non-ST mode

Previous changes were fixes for MED-native, non ST-compatible pitch slides.
In non-ST mode volume and pitch slides are computed in all frames.

To check: probably vibrato is updated in all frames too.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Stonecracker depacker cleanup

Removed error messages and incorrect assertion that fails when loading
synth-a-sysmic.med.stc.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Change S404 test to use a valid module file

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Minor refactor in MED synth

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>