- wl_proxy_add_listener: return -1 on NULL proxy (was page fault at null+8)
- wl_proxy_get_version: return 0 on NULL proxy
- wl_proxy_get_display: return NULL on NULL proxy
- All keep fprintf diagnostics for caller identification
This is the definitive fix for the Qt6 Wayland crash. Instead of
page-faulting at proxy->object.implementation (offset 8 from NULL),
libwayland now returns an error code. Qt6 will log errors but won't
crash — the Wayland session can initialize even with broken proxies.
vasilito
8883184f47