馃崚 X11Locker: always call stayOnTop when receiving XCB_MAP_NOTIFY to fix black screen
If a window was shown up previously and is hidden for now with the background window together, m_allowedWindows will contain the window. When the window shows up again, it will also raise the background window. But when handling XCB_MAP_NOTIFY event from the background window, stayOnTop is not called, so the background window becomes the top window.
(cherry picked from commit 0b208d59)
Co-authored-by: Fushan Wen qydwhotmail@gmail.com