t7614: avoid hiding git's exit code in a pipe

t7614: avoid hiding git's exit code in a pipe

The exit code of the upstream command in a pipe is ignored, so in

	git cat-file commit HEAD | sed -e "1,/^\$/d" >actual

a crash of "git cat-file" would go unnoticed: the exit code of the
pipeline is that of "sed", which happily succeeds on empty input. The
test would thus pass even though "git cat-file" failed.

Write the output of "git cat-file" to a file first and run "sed" on
that file, so that the exit codes of both commands are checked by the
&&-chain.

Signed-off-by: Shlok Kulshreshtha <diy2903@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>