test-lib: fix GIT_TEST_SANITIZE_LEAK_LOG

When a test that leaks runs with GIT_TEST_SANITIZE_LEAK_LOG=true,
the test returns zero, which is not what we want.

In the if-else's chain we have in "check_test_results_san_file_", we
consider three variables: $passes_sanitize_leak, $sanitize_leak_check
and, implicitly, GIT_TEST_SANITIZE_LEAK_LOG (always set to "true" at
that point).

For the first two variables we have different considerations depending
on the value of $test_failure, which makes sense.  However, for the
third, GIT_TEST_SANITIZE_LEAK_LOG, we don't;  regardless of
$test_failure, we use "invert_exit_code=t" to produce a non-zero
return value.

That assumes "$test_failure" is always zero at that point.  But it
may not be:

   $ git checkout v2.40.1
   $ make test SANITIZE=leak T=t3200-branch.sh # this fails
   $ make test SANITIZE=leak GIT_TEST_SANITIZE_LEAK_LOG=true T=t3200-branch.sh # this succeeds
   [...]
   With GIT_TEST_SANITIZE_LEAK_LOG=true, our logs revealed a memory leak, exiting with a non-zero status!
   # faked up failures as TODO & now exiting with 0 due to --invert-exit-code

We need to use "invert_exit_code=t" only when "$test_failure" is zero.

Let's add the missing conditions in the if-else's chain to make it work
as expected.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Rubén Justo <rjusto@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -1269,9 +1269,12 @@ check_test_results_san_file_ () {
 	then
 		say "As TEST_PASSES_SANITIZE_LEAK=true isn't set the above leak is 'ok' with GIT_TEST_PASSING_SANITIZE_LEAK=check" &&
 		invert_exit_code=t
-	else
+	elif test "$test_failure" = 0
+	then
 		say "With GIT_TEST_SANITIZE_LEAK_LOG=true our logs revealed a memory leak, exit non-zero!" &&
 		invert_exit_code=t
+	else
+		say "With GIT_TEST_SANITIZE_LEAK_LOG=true our logs revealed a memory leak..."
 	fi
 }