Fix windowless splash won't removed while hovering back gesture.

The windowless surface can be add after transition ready in core, so
there can defer the check until transaction applied.

Flag: EXEMPT bugfix
Bug: 372230928
Test: create windowless splash instead of snapshot, verify windowless
splash get removed as soon as prepare back transition ready.

Change-Id: I306b1d936504c48bd83d2185a54ecbddd0720d3e