swaybar: when hiding bar, save old height to be restored upon reshow

Previously, when the bar was hidden, the height would be set to 0.
This meant that if the bar was empty upon reshow, it would not render
since the height was still 0, which made it seem there was a problem.
Now, the height is not reset, but the width is, to indicate upon reshow
that the layer surface needed reconfiguring.

swaybar/bar.c

@@ -367,7 +367,6 @@ static void destroy_layer_surface(struct swaybar_output *output) {
 	zwlr_layer_surface_v1_destroy(output->layer_surface);
 	wl_surface_attach(output->surface, NULL, 0, 0); // detach buffer
 	output->layer_surface = NULL;
-	output->height = 0;
 	output->width = 0;
 	output->frame_scheduled = false;
 }

swaybar/render.c

@@ -519,7 +519,7 @@ void render_frame(struct swaybar_output *output) {
 	if (config_height >= 0 && height < (uint32_t)config_height) {
 		height = config_height;
 	}
-	if (height != output->height) {
+	if (height != output->height || output->width == 0) {
 		// Reconfigure surface
 		zwlr_layer_surface_v1_set_size(output->layer_surface, 0, height);
 		if (strcmp(output->bar->config->mode, "dock") == 0) {