t/lib-git-daemon: fix signal checking

Test scripts checking 'git daemon' stop the daemon with a TERM signal, and the 'stop_git_daemon' helper checks the daemon's exit status to make sure that it indeed died because of that signal.

This check is bogus since 03c39b3458 (t/lib-git-daemon: use test_match_signal, 2016-06-24), for two reasons:

- Right after killing 'git daemon', 'stop_git_daemon' saves its exit status in a variable, but since 03c39b3458 the condition checking the exit status looks at '$?', which at this point is not the exit status of 'git daemon', but that of the variable assignment, i.e. it's always 0.

- The unexpected exit status should abort the whole test script with 'error', but it doesn't, because 03c39b3458 forgot to negate 'test_match_signal's exit status in the condition.

This patch fixes both issues.

---
 t/lib-git-daemon.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index edbea2d986..f98de95c15 100644
@@ -92,7 +92,7 @@ stop_git_daemon() {
 	kill "$GIT_DAEMON_PID"
 	wait "$GIT_DAEMON_PID" >&3 2>&4
 	ret=$?
-	if test_match_signal 15 $?
+	if ! test_match_signal 15 $ret
 	then
 		error "git daemon exited with status: $ret"
 	fi

2.20.0.rc1.149.g55c2c038c2

Oof. Who says two wrongs don't make a right? :)

Thanks for catching this, and the patch looks obviously correct.

I peeked at the other test_match_signal conversions from that era, and they all look sane.

-Peff