t3600: fix broken "choking git rm" test

The test 'choking "git rm" should not let it die with cruft' is supposed to check 'git rm's behavior when interrupted by provoking a SIGPIPE while 'git rm' is busily deleting files from a specially crafted index. This test is silently broken for the following reasons: - The test crafts a special index by feeding a large number of index entries with null shas to 'git update-index --index-info'. It was OK back then when this test was introduced in commit 0693f9ddad (Make sure lockfiles are unlocked when dying on SIGPIPE, 2008-12-18), but since commit 4337b5856f (do not write null sha1s to on-disk index, 2012-07-28) null shas are not allowed in the on-disk index causing 'git update-index' to error out. - The barfing 'git update-index --index-info' should fail the test, but it remains unnoticed because of the severely broken && chain: the test's result depends solely on whether there is a stale lock file left behind, but after 'git update-index' errors out 'git rm' won't be executed at all. To fix this test feed only non-null shas to 'git update-index' and restore the && chain (partly by adding a missing && and by using the test_when_finished helper instead of manual cleanup). Signed-off-by: SZEDER Gábor <szeder@ira.uka.de> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>