Reduce some redundant steps

1. When |frame->pendingDirty.isEmpty()| is executed there, it must not be empty. Because the judgment has been made at the beginning of the applyRenderNodeTransform method.

2. When |dirty->isEmpty()|, |dirty->setIWH(frame.width(), frame.height());| can be returned directly after execution. There is no need to judge bufferAge, and subsequent steps are redundant. Because the maximum range of dirty is [0, 0, frame.width(), frame.height()]

Change-Id: Iccb3d39e4139c26ed5e7e24c39d1e141cb380dab
Signed-off-by: Liangliang Sui <coolsui.coding@gmail.com>