Fix scratchpad related crashes

* Was crashing when a view was moved to the scratchpad (prev focus had
no parent).
* Was crashing when a hidden scratchpad view unmaps because it has no
workspace.

sway/input/seat.c

@@ -618,7 +618,10 @@ void seat_set_focus_warp(struct sway_seat *seat, struct sway_node *node,
 	if (last_focus) {
 		seat_send_unfocus(last_focus, seat);
 		node_set_dirty(last_focus);
-		node_set_dirty(node_get_parent(last_focus));
+		struct sway_node *parent = node_get_parent(last_focus);
+		if (parent) {
+			node_set_dirty(parent);
+		}
 	}
 
 	// Put the container parents on the focus stack, then the workspace, then

sway/tree/view.c

@@ -560,11 +560,11 @@ void view_unmap(struct sway_view *view) {
 	container_begin_destroy(view->container);
 	if (parent) {
 		container_reap_empty(parent);
-	} else {
+	} else if (ws) {
 		workspace_consider_destroy(ws);
 	}
 
-	if (!ws->node.destroying) {
+	if (ws && !ws->node.destroying) {
 		arrange_workspace(ws);
 		workspace_detect_urgent(ws);
 	}