client: fix double removal of client on job file open failure

client: fix double removal of client on job file open failure

If fio is invoked as a client and the job file does not exist, it
will exit ala:

fio: job file <x.fio> open: No such file or directory
fio: client.c:240: remove_client: Assertion `client->refs' failed.

because the break path ends up doing the removal twice. Fix that
to only remove it once, so we don't trigger the assert.

Signed-off-by: Jens Axboe <axboe@fb.com>