Backport to 1.20 “xwayland: Delete all frame_callback_list nodes in xwl_unrealize_window”

We were only calling xwl_present_unrealize_window for the toplevel window, but the list can contain entries from child windows as well, in which case we were leaving dangling pointers to freed memory.

Closes: #1000 (closed) Fixes: c5067fea "xwayland: Use single frame callback for Present flips and normal updates" Reviewed-by: Olivier Fourdan ofourdan@redhat.com Tested-by: Olivier Fourdan ofourdan@redhat.com (cherry picked from commit 5e915873)