virsh: Fix a wrong check in cmdEcho()
virsh: Fix a wrong check in cmdEcho()

What should be checked here is xmlbuf rather than buf.

VenkatDatta/libvirt,eskultety/libvirt,taget/libvirt,libvirt/libvirt,agx/libvirt,eskultety/libvirt,jfehlig/libvirt,cbosdo/libvirt,datto/libvirt,shugaoye/libvirt,taget/libvirt,nertpinx/libvirt,shugaoye/libvirt,jfehlig/libvirt,elmarco/libvirt,eskultety/libvirt,rlaager/libvirt,fabianfreyer/libvirt,eskultety/libvirt,jfehlig/libvirt,olafhering/libvirt,shugaoye/libvirt,libvirt/libvirt,zhlcindy/libvirt-1.1.4-maintain,libvirt/libvirt,shugaoye/libvirt,cbosdo/libvirt,andreabolognani/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,zhlcindy/libvirt-1.1.4-maintain,jardasgit/libvirt,agx/libvirt,nertpinx/libvirt,olafhering/libvirt,zippy2/libvirt,jardasgit/libvirt,elmarco/libvirt,elmarco/libvirt,rlaager/libvirt,cbosdo/libvirt,fabianfreyer/libvirt,zippy2/libvirt,shugaoye/libvirt,nertpinx/libvirt,crobinso/libvirt,crobinso/libvirt,datto/libvirt,nertpinx/libvirt,elmarco/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,agx/libvirt,agx/libvirt,taget/libvirt,cbosdo/libvirt,nertpinx/libvirt,libvirt/libvirt,cbosdo/libvirt,zippy2/libvirt,elmarco/libvirt,olafhering/libvirt,rlaager/libvirt,rlaager/libvirt,agx/libvirt,eskultety/libvirt,fabianfreyer/libvirt,crobinso/libvirt,taget/libvirt,jardasgit/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,rlaager/libvirt,datto/libvirt,zhlcindy/libvirt-1.1.4-maintain,zippy2/libvirt,jardasgit/libvirt,taget/libvirt,datto/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,olafhering/libvirt,crobinso/libvirt,datto/libvirt,zhlcindy/libvirt-1.1.4-maintain,zhlcindy/libvirt-1.1.4-maintain