Michel Dänzer authored Jul 22, 2020 and Lyude Paul committed Jul 22, 2020

In the log of the commit below, I claimed this wasn't necessary on the
1.20 branch, but this turned out to be wrong: It meant that
event->buffer could already be destroyed in xwl_present_free_event,
resulting in use-after-free and likely a crash.

Fixes: 22c0808a "xwayland: Free all remaining events in
                     xwl_present_cleanup"