fio: Fix for new file creation

fio fails to create new file and just comes out without doing anything..
This happens only when you are creating file freshly.

./fio ../jobfile/jobfile.test
job1: (g=0): rw=randrw, bs=8K-8K/8K-8K, ioengine=sync, iodepth=1
Starting 1 process

Run status group 0 (all jobs):

Disk stats (read/write):
  sda: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%

jobfile:

[global]
 bs=8k
 iodepth_batch=1
 randrepeat=1
 size=100m
 [job1]
 ioengine=sync
 rw=randrw
 filename=newfile

Manually bisected it to commit 509eab12448823a8eefbe925804b5308ee63bf5e
Here is the patch which fixed the issue for me. Please review and apply.
In case of new file "f->io_size > f->real_file_size" becomes true, since
f->real_file_size is 0.

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