Fix scratchpad logic for floating windows

When a tiled window is sent to the scratchpad, we want to use sane
defaults, which is to center it and resize it to the default.

For floating windows, we want to use their existing geometry.

sway/tree/root.c

@@ -61,9 +61,14 @@ void root_scratchpad_add_container(struct sway_container *con) {
 
 	struct sway_container *parent = con->parent;
 	struct sway_workspace *workspace = con->workspace;
-	container_set_floating(con, true);
-	container_floating_set_default_size(con);
-	container_floating_move_to_center(con);
+
+	// When a tiled window is sent to scratchpad, center and resize it.
+	if (!container_is_floating(con)) {
+		container_set_floating(con, true);
+		container_floating_set_default_size(con);
+		container_floating_move_to_center(con);
+	}
+
 	container_detach(con);
 	con->scratchpad = true;
 	list_add(root->scratchpad, con);