This eliminates the CRITICAL, which was harmless anyway.
As discussed in the issue, there are more issues:
1. The "shift-start" action is not documented in the user manual.
2. The "shift-start" action quietly does nothing in the case
it has nothing to do. Better GUI would be to disable the menu item in that case.
3. The "shift-start" action is non-intuitive, even bizarre.
It could probably be eliminated.
I myself don't understand the use case, and confused it for Path>Reverse.
An alternative fix is to disable the menu item when a handle is the operand.
This fix is better because it gives the user more places to RMB a context menu,
and the context menu mutates less.
Probably needs backport to 2.10.
46c9949b7e