numa: fix assumption in virNumaNodeIsAvailable()

numa: fix assumption in virNumaNodeIsAvailable()

When compiled without full numa support, the stub function for
virNumaNodeIsAvailable() just checks whether specified node is in range
<0, max); where max is maximum NUMA node available on the host.  But
because the maximum node number is the highest usabe number (and not the
count of nodes), the check is incorrect as it should check whether the
specified node is in range <0, max> instead.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>