Fix "break delete --disabled" with no arguments.
The code that figured out which breakpoints to delete was supposed
to set the result status if it found breakpoints, and then the code
that actually deleted them checked that the result's status was set.
The code for "break delete --disabled" failed to set the status if
no "protected" breakpoints were provided. This was a confusing way
to implement this, so I reworked it with early returns so it was less
error prone, and added a test case for the no arguments case.