get_screen_cons() was gated on DISPLAY being set, which only ever happens on
Linux, so headful runs on Windows and macOS generated fingerprints with no
monitor bound at all.
Fixes#425
headless='virtual' reaches launch_options as headless=False with
virtual_display set (async_api rewrites it), so the headful gate fired and
clamped the fingerprint to Xvfb's 1x1 stub. fix_screen_no_taskbar then drove
availHeight to -39 and validate_config rejected the launch outright.