SurfaceFlinger: Do not capture rounded corners on screenshots

Fixes a regression that arose because we no longer properly
checked for the layerStack when traversing the layers for
screenshotting.

Bug: 72111097
Test: Take screenshot, verify rounded corner overlays do not appear.
Change-Id: Ifc178247fe5b72376c56a0a1d347d7bd04784cae
1 file changed