The IPA.entity_select_widget doesn't show the undo button properly when the filter is changed for the first time.

Steps to reproduce:
1. In Web UI go to IPA Server -> Delegation.
2. Click one of the existing entries.
3. Click 'add group filter' next to the 'User group' or 'Member user group' field.
4. Change the value of the filter. The drop down list will become blank, but the undo button doesn't appear.
5. Change the value of the filter again. Now the undo button will appear.

Expected result: in step #4 the undo button should appear.