virDomainDeviceAliasIsUserAlias: tolerate NULL
virDomainDeviceAliasIsUserAlias: tolerate NULL

Do not crash in virDomainDeviceInfoParseXML if someone provides
an 'alias' element without a 'name' attribute.

Signed-off-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

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