t1450: fix testcases that were wrongly expecting failure

t1450: fix testcases that were wrongly expecting failure

Almost exactly a year ago in 02a6552 (Test fsck a bit harder), I
introduced two testcases that were expecting failure.

However, the only bug was that the testcases wrote *blobs* because I
forgot to pass -t tag to hash-object.  Fix this, and then adjust the
rest of the test to properly check the result.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>