Fix crash when loading project with missing peak controller effect

[PhysSong]

Fixes #4060.

[PhysSong]

Loading such project will create dummy connections where the broken connection was. Would it be better to remove them or leave them? Leaving will let user easily notice there were connections, but it leads to weird connections when re-saved.
I will add a check for dummy connection in saving code, and removal of them if needed.

[zonkmachine]

I'm only able to reproduce #4060 with the AppImages but the test build of this PR worked at a more casual test. I have problems building right now but may test this more later. I don't know why I see #4060 only with the AppImages.

[PhysSong]

Issues with dummy connections:

• Lock model value
• Cause wrong connections to be added when saving/reopening

So I think broken connections should be removed when loading project.

[zonkmachine]

I've tested this some more and the demo files from #4060 opens up with no problems. I'm also fine with removing broken connections. It's the manly way to go about the issue. Just nuke it. I think you should go ahead and merge this if/when you're happy with it. I bumped #devtalk for a review and there's been no objections.