Fix `unused-result' warnings.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
diff --git a/clients/dnd.c b/clients/dnd.c
index e3d3c34..8e67dc4 100644
--- a/clients/dnd.c
+++ b/clients/dnd.c
@@ -272,7 +272,9 @@
 	dnd_flower_message.x_offset = dnd_drag->x_offset;
 	dnd_flower_message.y_offset = dnd_drag->y_offset;
 
-	write(fd, &dnd_flower_message, sizeof dnd_flower_message);
+	if (write(fd, &dnd_flower_message, sizeof dnd_flower_message) < 0)
+		abort();
+
 	close(fd);
 }