xfs: test mkfs.xfs whether terminate getsubopt arrays properly

xfs: test mkfs.xfs whether terminate getsubopt arrays properly

When I run xfs/144 manually, the step as below:
mkfs.xfs -f -d agcount=3200,size=6366g -d file,n

I accidentally pressed the Enter key, it triggers Segmentation fault.
Then I found Darrick has fixed this one week ago. So add this test.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>