Xi: ProcXIGetSelectedEvents needs to use unswapped length to send reply

CVE-2024-31080

Reported-by: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=69762


Fixes: 53e821ab ("Xi: add request processing for XIGetSelectedEvents.")
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Part-of: <!1463>