reflog: fix 'show' subcommand's argv

reflog: fix 'show' subcommand's argv

cmd_reflog() invokes parse_options() with PARSE_OPT_KEEP_ARGV0, but it
doesn't account for the retained argv[0] before invoking
cmd_reflog_show() to handle the 'git reflog show' subcommand.
Consequently, cmd_reflog_show() always gets an 'argv' array starting
with elements argv[0]="reflog" and argv[1]="show".

Strip the name of the git command from the 'argv' array before passing
it to the function handling the 'show' subcommand.

There is no user-visible bug here, because cmd_reflog_show() doesn't
have any options or parameters of its own.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>