seat_create: set initial focus for added seats

This sets the initial focus for all seats other than the first seat,
which gets it focus on launch. The ensures that all seats have something
focused.

sway/input/seat.c

@@ -357,6 +357,14 @@ struct sway_seat *seat_create(const char *seat_name) {
 	root_for_each_workspace(collect_focus_workspace_iter, seat);
 	root_for_each_container(collect_focus_container_iter, seat);
 
+	if (!wl_list_empty(&server.input->seats)) {
+		// Since this is not the first seat, attempt to set initial focus
+		struct sway_seat *current_seat = input_manager_current_seat();
+		struct sway_node *current_focus =
+			seat_get_focus_inactive(current_seat, &root->node);
+		seat_set_focus(seat, current_focus);
+	}
+
 	wl_signal_add(&root->events.new_node, &seat->new_node);
 	seat->new_node.notify = handle_new_node;