tools: Fix wild memory allocations from c/s 250f0b4 and 85d78b4

These changesets cause the respective libxc functions to unconditonally
dereference their max_cpus/nodes parameters as part of initial memory
allocations.  It will fail at obtaining the correct number of cpus/nodes from
Xen, as the guest handles will not be NULL.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

tools/python/xen/lowlevel/xc/xc.c

@@ -1221,7 +1221,7 @@ static PyObject *pyxc_getcpuinfo(XcObject *self, PyObject *args, PyObject *kwds)
 static PyObject *pyxc_topologyinfo(XcObject *self)
 {
     xc_cputopo_t *cputopo = NULL;
-    unsigned i, num_cpus;
+    unsigned i, num_cpus = 0;
     PyObject *ret_obj = NULL;
     PyObject *cpu_to_core_obj, *cpu_to_socket_obj, *cpu_to_node_obj;
 
@@ -1293,7 +1293,7 @@ out:
 
 static PyObject *pyxc_numainfo(XcObject *self)
 {
-    unsigned i, j, num_nodes;
+    unsigned i, j, num_nodes = 0;
     uint64_t free_heap;
     PyObject *ret_obj = NULL, *node_to_node_dist_list_obj;
     PyObject *node_to_memsize_obj, *node_to_memfree_obj;