Slurs from one voice to another don't save properly
Discovered in the course of fixing Issue #24245: Slur attaches to note in wrong voice after save/load. Slurs neither save nor restore correctly when the slur finishes on a different voice from the one it starts in.
The fix for #24245: Slur attaches to note in wrong voice after save/load now allows slurs within a voice to be restored correctly. The fix for this issue completes the solution.