qemu: Do not pass negative ncpus to virCapabilitiesClearHostNUMACellCPUTopology

It won't cause any harm as cpus is NULL when we pass a negative ncpus,
but doing so when the function expects unsigned value is not right.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/conf/capabilities.c

@@ -1954,6 +1954,7 @@ virCapabilitiesHostNUMAInitReal(virCapsHostNUMA *caps)
             if (ncpus == -2)
                 continue;
 
+            ncpus = 0;
             goto cleanup;
         }