webadmin: Revert findbugs fix that caused regression

A findbugs fix removed a "redundant" null check, which caused the
Setup Host Networks dialog to malfunction. There was indeed a
redundant null check, but not the one that was removed.

Bug-Url: https://bugzilla.redhat.com/975886

Change-Id: I8b19c8588168281734e76e08ce98105ae5721941
Signed-off-by: Lior Vernia <lvernia@redhat.com>