t5313-pack-bounds-checks.sh flaky?

Hi Peff,

t5313.7 failed recently on master [1]. Are you aware of any flaky parts in this test?

Here is the output:

expecting success: 
	# We need two objects here, so we can plausibly require
	# an extended table (if the first object were larger than 2^31).
	do_pack "$object $(git rev-parse HEAD)" --index-version=2 &&

	# We have to make extra room for the table, so we cannot
	# just munge in place as usual.
	{
		dd if=$idx bs=1 count=$(($(ofs_table 2) + 4)) &&
		printf "\200\0\0\0" &&
		printf "\377\0\0\0\0\0\0\0" &&
		dd if=$idx bs=1 skip=$(extended_table 2)
	} >tmp &&
	mv tmp "$idx" &&
	clear_base &&
	test_must_fail git cat-file blob $object &&
	test_must_fail git index-pack --verify $pack

1084+0 records in 1084+0 records out 1084 bytes (1.1 kB) copied, 0.00119315 s, 909 kB/s 40+0 records in 40+0 records out 40 bytes (40 B) copied, 6.9825e-05 s, 573 kB/s 74 test_must_fail: command succeeded: git cat-file blob fff0a2476aa5c8e60a3ef21cfc66e0cc670920be

Cheers, Lars

[1] https://travis-ci.org/git/git/jobs/239451919