Set focus_inactive on a sibling when a container closes in an inactive workspace

To reproduce the problem, create layout
H[view V[view view view-focused]], then switch to another workspace and
have the previously focused view in the vsplit close (eg. using
criteria, or an mpv video finishing). Return to the workspace using
`$mod+<num>` and the entire vsplit would be focused. This happens
because handle_seat_node_destroy would only set a new focus if the
currently focused view or a parent was being destroyed. To fix it, it
needs to set a sibling of the destroying container to focus_inactive
regardless of the current focus, then restore current focus if needed.

This patch changes the function accordingly. Additionally:

* The function now makes an early return if the node being destroyed is
a workspace.
* set_focus has been renamed to needs_new_focus. This variable is true
if the head focus needs to be changed.

sway/input/seat.c

@@ -144,14 +144,20 @@ static void handle_seat_node_destroy(struct wl_listener *listener, void *data) {
 	struct sway_node *parent = node_get_parent(node);
 	struct sway_node *focus = seat_get_focus(seat);
 
-	bool set_focus =
-		focus != NULL &&
-		(focus == node || node_has_ancestor(focus, node)) &&
-		node->type == N_CONTAINER;
+	if (node->type == N_WORKSPACE) {
+		seat_node_destroy(seat_node);
+		return;
+	}
+
+	// Even though the container being destroyed might be nowhere near the
+	// focused container, we still need to set focus_inactive on a sibling of
+	// the container being destroyed.
+	bool needs_new_focus = focus &&
+		(focus == node || node_has_ancestor(focus, node));
 
 	seat_node_destroy(seat_node);
 
-	if (set_focus) {
+	// Find new focus_inactive (ie. sibling, or workspace if no siblings left)
 	struct sway_node *next_focus = NULL;
 	while (next_focus == NULL) {
 		struct sway_container *con =
@@ -166,10 +172,15 @@ static void handle_seat_node_destroy(struct wl_listener *listener, void *data) {
 		parent = node_get_parent(parent);
 	}
 
-		// the structure change might have caused it to move up to the top of
+	if (needs_new_focus) {
+		// The structure change might have caused it to move up to the top of
 		// the focus stack without sending focus notifications to the view
 		seat_send_focus(next_focus, seat);
 		seat_set_focus(seat, next_focus);
+	} else {
+		// Setting focus_inactive
+		seat_set_focus_warp(seat, next_focus, false, false);
+		seat_set_focus_warp(seat, focus, false, false);
 	}
 }