hash-object: fix a trivial leak in --path

Fix a memory leak that happened when the --path option was
provided. This leak has been with us ever since the option was added
in 3970243150 (add --path option to git hash-object, 2008-08-03).

We can now mark "t1007-hash-object.sh" as passing when git is compiled
with SANITIZE=leak. It'll now run in the the
"GIT_TEST_PASSING_SANITIZE_LEAK=true" test mode (the "linux-leaks" CI
target).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1007-hash-object.sh

@@ -2,6 +2,7 @@
 
 test_description="git hash-object"
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 echo_without_newline() {