wayland: roundtrip: log error and abort when wl_display_roundtrip() fails

ayl_roundtrip() has the following code:

    wl_display_roundtrip(wayl->display);

    while (wl_display_prepare_read(wayl->display) != 0)
        wl_display_dispatch_pending(wayl->display);
    wayl_flush(wayl);

If the first wl_display_roundtrip() fails, for example because the
Wayland socket has been closed, we may get stuck in the while-loop.

This happens if the read queue isn’t empty, in which case
wl_display_prepare_read() will return -1 and we’ll continue trying to
dispatch the pending events forever, never succeeding since the socket
is gone.

Closes #542

CHANGELOG.md

@@ -126,6 +126,9 @@
 * Rare occurrences where the window did not close when the shell
   exited. Only seen on FreeBSD
   (https://codeberg.org/dnkl/foot/issues/534)
+* Foot process(es) sometimes remaining, using 100% CPU, when closing
+  multiple foot windows at the same time
+  (https://codeberg.org/dnkl/foot/issues/542).
 
 
 ### Security