[MU4 Issue] Crash when trying to create a new score based on a custom template with instruments changes

[metasekk]

Describe the bug
MuseScore4 crashes when trying to create a new score based on a custom template containing at least one instrument change in it.

To Reproduce
Steps to reproduce the behavior:

1. Create a new score
2. Set at least one mid-staff instrument change (with the Change Instrument text) on an arbitrary staff
3. Save the score in the Template directory of your Musescore4 working directory.
4. Try to create a new score based on it.
5. See Musescore4 crash.

Expected behavior
The new score should be created without a crash, regardless of the content of the template.

Screenshots
I provide a video of the crash.

Platform information

• OS: Windows 10 Version 22H2, 64 bits, x64-based processor
• Tested on: MuseScore Release version (64-bit): 4.0.0-223472200 with MuseSampler v.0.3.2

Additional context
It does not appear to be a critical issue, but it seems worth knowing about.

[bkunda]

Still reproducible in latest master.
Leaving as P2 for now as the triggers are not sufficiently frequent to affect most regular use cases.

[Jojo-Schmitz]

FWIW: Mu3 doesn't crash on this, but looses the instrument change

[mathesoncalum]

The repro steps for this one seem to have evolved slightly in the current master; the score can be created just fine but interacting with it (e.g. adding some notes) causes a crash.

I'm fairly certain the root cause is the same though, #20102 should rectify.