udev_device_get_devpath might return NULL
udev_device_get_devpath might return NULL

Fix crash on strdup in that case.

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