apparmor: fix leak of null profile name if profile allocation fails

[ Upstream commit 4633307e ]

Fixes: d07881d2 ("apparmor: move new_null_profile to after profile lookup fns()")
Reported-by: Seth Arnold <seth.arnold@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>