SendDebugScreenshot ignores the descriptor entirely and reads the display
framebuffer from the GPU, so filling one in was theatre - and it computed a
pointer from the display address, which is zero whenever the shell has the
display switched off.
Also reset g_screenshotSaved per test, so a test that emits its own screenshot
doesn't stop the next one getting the end-of-run capture, and clear the sceReg
open count on shutdown to match init.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>