ui: make template - NPE in wrong display type

when creating a template from a VM with a display type that is not
supported the os we get NPE when setting the VMs display type to the
template.
(caused by upgrading an old version)

Bug-Url: https://bugzilla.redhat.com/1111551
Change-Id: I6921c7f620c9de2e3cc0293c096d48418f509f55
Signed-off-by: Shahar Havivi <shaharh@redhat.com>