virsh: Do not try to free domain if it is NULL
virsh: Do not try to free domain if it is NULL

Without these patch, there will be error like below if domain
is NULL.

error: invalid domain pointer in virDomainFree

Which is useless.

nertpinx/libvirt,bjzhang/libvirt,foomango/libvirt,olafhering/libvirt,emaste/libvirt,rlaager/libvirt,eskultety/libvirt,olafhering/libvirt,crobinso/libvirt,nertpinx/libvirt,jeckersb/libvirt,taget/libvirt,eskultety/libvirt,zippy2/libvirt,libvirt/libvirt,wiedi/libvirt,novel/fbsd-libvirt,elmarco/libvirt,jfehlig/libvirt,andreabolognani/libvirt,leilihh/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,datto/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,siboulet/libvirt-openvz,shugaoye/libvirt,kantai/libvirt-vfork,nertpinx/libvirt,iam-TJ/libvirt,elmarco/libvirt,zhlcindy/libvirt-1.1.4-maintain,kantai/libvirt-vfork,kantai/libvirt-vfork,rmarwaha/libvirt,wiedi/libvirt,libvirt/libvirt,shugaoye/libvirt,elmarco/libvirt,dumbbell/libvirt,warewolf/libvirt,rlaager/libvirt,VenkatDatta/libvirt,iam-TJ/libvirt,usc-isi/libvirt,cbosdo/libvirt,emaste/libvirt,taget/libvirt,emaste/libvirt,siboulet/libvirt-openvz,novel/fbsd-libvirt,kantai/libvirt-vfork,zhlcindy/libvirt-1.1.4-maintain,fabianfreyer/libvirt,iam-TJ/libvirt,iam-TJ/libvirt,rmarwaha/libvirt1,bjzhang/libvirt,leilihh/libvirt,shugaoye/libvirt,danwent/libvirt-ovs,warewolf/libvirt,warewolf/libvirt,iam-TJ/libvirt,warewolf/libvirt,elmarco/libvirt,rmarwaha/libvirt1,agx/libvirt,fabianfreyer/libvirt,trainstack/libvirt,crobinso/libvirt,rmarwaha/libvirt,wiedi/libvirt,rlaager/libvirt,wiedi/libvirt,rmarwaha/libvirt1,dumbbell/libvirt,siboulet/libvirt-openvz,crobinso/libvirt,rmarwaha/libvirt1,jfehlig/libvirt,taget/libvirt,dumbbell/libvirt,rmarwaha/libvirt,wiedi/libvirt,fabianfreyer/libvirt,shugaoye/libvirt,nertpinx/libvirt,leilihh/libvirt,libvirt/libvirt,cbosdo/libvirt,rlaager/libvirt,emaste/libvirt,dumbbell/libvirt,datto/libvirt,agx/libvirt,soulxu/libvirt-xuhj,siboulet/libvirt-openvz,novel/fbsd-libvirt,warewolf/libvirt,eskultety/libvirt,rlaager/libvirt,danwent/libvirt-ovs,dumbbell/libvirt,danwent/libvirt-ovs,andreabolognani/libvirt,cbosdo/libvirt,trainstack/libvirt,datto/libvirt,fabianfreyer/libvirt,emaste/libvirt,danwent/libvirt-ovs,crobinso/libvirt,agx/libvirt,zhlcindy/libvirt-1.1.4-maintain,zhlcindy/libvirt-1.1.4-maintain,emaste/libvirt,taget/libvirt,eskultety/libvirt,jeckersb/libvirt,soulxu/libvirt-xuhj,iam-TJ/libvirt,wiedi/libvirt,soulxu/libvirt-xuhj,jardasgit/libvirt,soulxu/libvirt-xuhj,trainstack/libvirt,novel/fbsd-libvirt,foomango/libvirt,VenkatDatta/libvirt,rmarwaha/libvirt,danwent/libvirt-ovs,datto/libvirt,rmarwaha/libvirt1,novel/fbsd-libvirt,soulxu/libvirt-xuhj,VenkatDatta/libvirt,usc-isi/libvirt,jeckersb/libvirt,emaste/libvirt,jeckersb/libvirt,zhlcindy/libvirt-1.1.4-maintain,andreabolognani/libvirt,zippy2/libvirt,andreabolognani/libvirt,bjzhang/libvirt,dumbbell/libvirt,elmarco/libvirt,novel/fbsd-libvirt,iam-TJ/libvirt,foomango/libvirt,jardasgit/libvirt,agx/libvirt,novel/fbsd-libvirt,foomango/libvirt,jeckersb/libvirt,siboulet/libvirt-openvz,zippy2/libvirt,taget/libvirt,olafhering/libvirt,usc-isi/libvirt,kantai/libvirt-vfork,andreabolognani/libvirt,rmarwaha/libvirt,cbosdo/libvirt,jardasgit/libvirt,usc-isi/libvirt,trainstack/libvirt,olafhering/libvirt,jeckersb/libvirt,novel/fbsd-libvirt,rmarwaha/libvirt,jardasgit/libvirt,eskultety/libvirt,bjzhang/libvirt,zippy2/libvirt,leilihh/libvirt,cbosdo/libvirt,nertpinx/libvirt,libvirt/libvirt,wiedi/libvirt,rmarwaha/libvirt1,leilihh/libvirt,datto/libvirt,trainstack/libvirt,novel/fbsd-libvirt,bjzhang/libvirt,trainstack/libvirt,usc-isi/libvirt,trainstack/libvirt,warewolf/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,foomango/libvirt,warewolf/libvirt,agx/libvirt,leilihh/libvirt,jeckersb/libvirt,shugaoye/libvirt