Fix runtime of terse output

Fix runtime of terse output

Hi,

When I used fio with option of '--status-interval=1 --minimal' and 'random_distribution=zipf:1.2',
'runtime' of 2nd line was 18446744073709551345.
This value is -271 in int_64.

This is because 'runtime' was subtracted in function '__show_running_run_stats'.
If 'td->io_bytes' is 0 when this function was called,
and 'td->io_bytes' is not 0 when '__show_run_stats' returned,
'runtime' is subtracted by 'rt' even though 'runtime' have not added.

I fixed the problem by applying this patch to fio-2.2.13.

Regards
Shoichi

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