deselect after use if nothing was selected before

in AddRemoveBreaks and ResequenceRehersalMarks.
@MarcSabatella: this is what I meant in my comments to your PR #1525 

Also prevent ResequenceRehersalMarks to destroy a list selection, AddRemoveBreaks prevents that already, neither works or makes sense on a list selection.
Furthermore prevent a crash when running AddRemoveBreaks or SlashFill on an empty score
(for some reason ResequenceRehersalMarks and SlashRhythm don't have that issue).

transpose on list selection too, instead of destroying that selection.
Also deselect afterwards if nothing was selected before.