sequencer: update `done_nr' when skipping commands in a todo list
In a todo list, `done_nr' is the number of commands that were executed
or skipped, but skip_unnecessary_picks() did not update it.
This variable is mostly used by command prompts (ie. git-prompt.sh and
the like). As in the previous commit, this inconsistent behaviour is
not a problem yet, but it would start to matter at the end of this
series the same reason.
Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>