Don't create CE Layer when EffectLayer has nothing to draw.

If the EffectLayer has nothing to draw, it's essentially a container
layer. In that case, there's no need to create a CE Layer since nothing
will draw on screen.

This fixes the case where a VD is created for screenrecording. The first
few frames can be black because there's an effect layer in the hierarchy
with nothing to draw before the mirroring starts. When that happens,
the recording shows black frames. There's no need to render the
EffectLayer since it doesn't actually have content

Fixes: 222749939
Test: Screenrecord no black frames at the start.
Change-Id: Iec720810eaad923a4045b8f1b73b088ada86cfd1