Fix crash on deleting "system object" staff

correction

Author: mike-spa

src/engraving/libmscore/edit.cpp

@@ -5144,6 +5144,8 @@ void Score::undoRemoveStaff(Staff* staff)
 
     staff->undoUnlink();
 
+    mu::remove_if(systemObjectStaves, [staff](Staff* s){ return s == staff; });
+
     undo(new RemoveStaff(staff));
 }