wayland: attempt to log protocol errors on failure to flush

When failing to flush, and the error is EPIPE, attempt to read and
dispatch events. This ensures protocol errors are logged.

wayland.c

@@ -2247,7 +2247,14 @@ wayl_flush(struct wayland *wayl)
         }
 
         if (errno != EAGAIN) {
-            LOG_ERRNO("failed to flush wayland socket");
+            const int saved_errno = errno;
+
+            if (errno == EPIPE) {
+                wl_display_read_events(wayl->display);
+                wl_display_dispatch_pending(wayl->display);
+            }
+
+            LOG_ERRNO_P(saved_errno, "failed to flush wayland socket");
             return;
         }