vnuma_nodes missing pnode 0

[Jim Fehlig <jfehlig@xxxxxxxx>]

Hi All,

While fixing [1] a recent downstream libvirt build failure against 4.17 rc3, I 
noticed the json representation of libxl_vnode_info omits pnode when value is 0. 
The problem can be seen by starting a VM containing the following vnuma config
vnuma = [ [ "pnode=0", "size=2048", "vcpus=0", "vdistances=10,20" ], [ 
"pnode=1", "size=2048", "vcpus=1", "vdistances=20,10" ] ]
The json representation for this config does not contain pnode 0

               "vnuma_nodes": [
                    {
                        "memkb": 2097152,
                        "distances": [
                            10,
                            20
                        ],
                        "vcpus": [
                            0
                        ]
                    },
                    {
                        "memkb": 2097152,
                        "distances": [
                            20,
                            10
                        ],
                        "pnode": 1,
                        "vcpus": [
                            1
                        ]
                    }
                ],

I'm not familiar with the code generator for the *_to_json functions, but with a 
hint I can probably cook up a patch :-).
Regards,
Jim

[1] https://listman.redhat.com/archives/libvir-list/2022-November/235745.html