llibeston/backend-x11: Tracking previous events over multiple calls

Version 2: Rather than providing a band-aid which detected when we still had a notify listener installed and re-init the linker entry to avoid corrupting the surface destory signal list, properly fix the issue in and handle previous events that spawn across multiple x11_backend_handle_event() calls.

Version 1: As seen with the x11 backend, we could get multiple focus_out events without actually getting a focus_in event, causing the destroy signal list to be corrupted, leading to a crash.

Fixes #650 (closed)

Suggested-by: Alexandros Frantzis alexandros.frantzis@collabora.com Reported-by: Alexandros Frantzis alexandros.frantzis@collabora.com Signed-off-by: Marius Vlad marius.vlad@collabora.com ~~