Re: [PATCH v3 4/7] sequencer: factor out part of pick_commits()

> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>
> This simplifies the next commit. If a pick fails we now return the error
> at the end of the loop body rather than returning early, a successful
> "edit" command continues to return early. There are three things to
> check to ensure that removing the early return for an error does not
> change the behavior of the code:
>
> (1) We could enter the block guarded by "if (reschedule)". This block
>     is not entered because "reschedlue" is always zero when picking a
>     commit.
>
> (2) We could enter the block guarded by
>     "else if (is_rebase_i(opts) &&  check_todo && !res)". This block is
>     not entered when returning an error because "res" is non-zero in
>     that case.
>
> (3) todo_list->current could be incremented before returning. That is
>     avoided by moving the increment which is of course a potential
>     change in behavior itself. The move is safe because none of the
>     callers look at todo_list after this function returns. Moving the
>     increment makes it clear we only want to advance the current item
>     if the command was successful.