virshDomainGetVcpuBitmap: Return bitmap when taking the fallback path

In case the specific VCPU states are not present in the XML we were
taking a fallback code path just noting that all cpus of the VM are
enabled.

This was broken by a mistake in a recent refactor where a 'goto cleanup'
was mistakenly replaced by a 'return NULL'. This broke reporting of cpus
and also caused a memory leak.

Return the fallback cpu map.

Fixes: bd1f40fe7d
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2004429
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Jonathon Jongsma <jjongsma@redhat.com>

tools/virsh-domain.c

@@ -6710,7 +6710,7 @@ virshDomainGetVcpuBitmap(vshControl *ctl,
         for (i = 0; i < curvcpus; i++)
             ignore_value(virBitmapSetBit(ret, i));
 
-        return NULL;
+        return ret;
     }
 
     for (i = 0; i < nnodes; i++) {