Saving Instrument does not Save midi configuration

Nobody has claimed this yet.

### System Information

Windows 11

### LMMS Version(s)

lmms-1.3.0-alpha.1.738+g23db892d5-mingw-win64

### Most Recent Working Version

_No response_

### Bug Summary

When i save an instrument as a .xpf and then load it the information in the "MIDI" tab does is not correct. It is always the default value instead of the value that was present when the .xpf was made.

### Expected Behaviour

The values in the "MIDI" tab of an instrument loaded from a .xpf should the the same as they are in the instrument the .xpf was made from.

### Steps To Reproduce

Open an instrument.
Go to the "MIDI" tab.
Change one of the values (Example: change fixed note velocity to 100).
Click on the save button.
Save the instrument as a .xpf.
Load the instrument into the project.
Open the new instrument and check the "MIDI" tab.

### Logs

Click to expand

### Screenshots / Minimum Reproducible Project

_No response_

### Please search the issue tracker for existing bug reports before submitting your own.

- [X] I have searched all existing issues and confirmed that this is not a duplicate.

Start by tracing how instruments are saved to and loaded from .xpf files, focusing on the MIDI tab values described in the reproduction steps. Reproduce the issue by changing fixed note velocity, saving and reloading the instrument, then verify that the MIDI settings match the original values.

Written by the indexing model from the issue text.