Fix the issue that renderEngine bails out too early.

- Remove the check about empty layer, because bailing out too early will
  cause dirty buffers to be re-used before they get cleared.
- Test locally but hold off adding corresponding test until ANGLE side
  fixes the issue of clearing a new created buffer.

Bug: 233052879
Test: librenderengine_test, and test locally with new test case
Change-Id: Ie1a04b1ce6b691f99555f60d680846c8ab4f1f97