webadmin: Fix NPE in Host dialog

Fixed NPE caused by http://gerrit.ovirt.org/#/c/32021/

Change-Id: I6d060d60a9ebd793d48275283741fabfee600224
Bug-Url: https://bugzilla.redhat.com/1133540
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>