window: Workaround a stuck frame callback on the cursor surface

window: Workaround a stuck frame callback on the cursor surface

It is possible that a client loses the focus between receiving a
pointer.enter event and sending a pointer.set_cursor request. In that
case, the cursor surface might not be mapped and the frame callback
requested on it will never trigger.

Work around this by trying to remap the cursor surface whenever there
is a frame callback and the serial for the enter event is higher than
the cursor serial.