wedamdin: NPE when removing label from interface/bond

When removing label from a nic with no 'network labels' attached to it
there was NPE. Added safe check to fix this issue.

Change-Id: I18619a212503731586c68dc414e51ae12e52fefa
Bug-Url: https://bugzilla.redhat.com/1063762
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>