Fix reading NULL Surfaces from Parcels

Writing a NULL Surface was being read as a non-NULL Surface with NULL
mGraphicBufferProducer. Before the SurfaceTextureClient -> Surface
refactoring, you'd get a NULL Surface, and some code relies on that.

Bug: 8291161
Change-Id: I477bfe8882693e53a5f604a3d2c9e3cfe24473b4