[BUG] git config --unset is not idempotent

[Arturo Seijas Fernandez <arturo.seijas@xxxxxxxxxxxxx>]

The command "git config --unset [option]" is not idempotent. It is
currently returning a success  code when the property had already been
set and a 5 error code otherwise.

I would expect the error code to be set according to the current state
when compared to the target state, regardless of the previous state of
the option.

Thank you,

Arturo Seijas