Differentiate empty UI from default in recents Go

Use the "empty" drawable as the initial UI until the recents task list
and order is loaded, then switch to default/filled UI.

Bug: 114136250
Test: Manual test; see empty UI when loading takes time
Change-Id: I85b72e6d40d7224b28217cbf4e05515ec1e9451b
(cherry picked from commit a2c4200c)