module-jack-sink/source: protect against null return in jack_get_ports

module-jack-sink/source: protect against null return in jack_get_ports

Just picking up a crash report from Ubuntu, here's the result.

--
David Henningsson, Canonical Ltd.
http://launchpad.net/~diwic

From 934c52c79bb6faed56a64d6e15f9b285f687afee Mon Sep 17 00:00:00 2001
From: David Henningsson <david.henningsson@canonical.com>
Date: Mon, 28 Mar 2011 14:30:44 +0200
Subject: [PATCH] module-jack-sink/source: protect against null return in jack_get_ports

According to jack_get_ports documentation, it seems like returning NULL
is valid, and that it should be freed using jack_free.

Reported-by: Grayson Peddie
BugLink: http://bugs.launchpad.net/bugs/733424
Signed-off-by: David Henningsson <david.henningsson@canonical.com>