core: NPE when getVMFullList returns no vm information

When getVMFullList fetches no information the code fails with NPE.

Bug-Url: https://bugzilla.redhat.com/1135959
Change-Id: Iefbf71dd19bc6c759f1ef2ac02a2f6136146989f
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>