Don't queue buffer if nothing new to draw in Display

The current logic only checks if dirty is not empty, but doesn't account
for no content changing. Instead use the same logic that's in
beginFrame to compute mustRecompute and use that when determining if the
display should queue a buffer.

This fixes an issue where a Displays first few frames could be black
until the content is loaded.

Bug: 239888440
Test: First frame from screenrecord is no longer black
Change-Id: Ibb568302bf2d50db167a1f9ca76a0f37e2c65bf5
(cherry picked from commit 09fa1d66)