qemu: prevent invalid reads in qemuAssignDevicePCISlots
qemu: prevent invalid reads in qemuAssignDevicePCISlots

Don't reserve slot 2 for video if the machine has no PCI buses.
Error out when the user specifies a video device without
a PCI address when there are no PCI buses.

(This wouldn't work on a machine with no PCI bus anyway since
we do add PCI addresses for video devices to the command line)

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