virsh: do not assign negative values to niothreads
virsh: do not assign negative values to niothreads

Use a temporary 'rc' variable to avoid comparing signed
and unsigned integers in the cleanup section.

Bug introduced by commit 3072ded which added the comparison against
the unsigned 'i'.

Also make niothreads size_t to mark that it should be unsigned.

Signed-off-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>
Reviewed-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

crobinso/libvirt,olafhering/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,jfehlig/libvirt,nertpinx/libvirt,jardasgit/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt,olafhering/libvirt,libvirt/libvirt,olafhering/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,eskultety/libvirt,eskultety/libvirt,andreabolognani/libvirt,eskultety/libvirt,fabianfreyer/libvirt,zippy2/libvirt,olafhering/libvirt,nertpinx/libvirt,crobinso/libvirt,eskultety/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,nertpinx/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,crobinso/libvirt,eskultety/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,jardasgit/libvirt,andreabolognani/libvirt,jfehlig/libvirt,jfehlig/libvirt,andreabolognani/libvirt,zippy2/libvirt,zippy2/libvirt