virsh: Properly terminate string list in virshDomainInterfaceSourceModeCompleter()
virsh: Properly terminate string list in virshDomainInterfaceSourceModeCompleter()

A completer must return a NULL terminated list of strings, which
means that when dealing with enums, it has to allocate one
pointer more than the value of VIR_XXX_LAST. But this is not
honoured in virshDomainInterfaceSourceModeCompleter() leading to
out of bounds read.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

zippy2/libvirt,jfehlig/libvirt,crobinso/libvirt,zippy2/libvirt,jfehlig/libvirt,zippy2/libvirt,jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt,crobinso/libvirt,olafhering/libvirt,olafhering/libvirt,olafhering/libvirt,crobinso/libvirt,crobinso/libvirt