compositor: remove unnecessary wlr_surface.has_buffer

No need to store this bit, we can infer it from buffer_width and
buffer_height.

include/wlr/types/wlr_compositor.h

@@ -218,7 +218,6 @@ struct wlr_surface {
 	bool unmap_commit;
 
 	bool opaque;
-	bool has_buffer;
 
 	int32_t preferred_buffer_scale;
 	bool preferred_buffer_transform_sent;

types/wlr_compositor.c

@@ -341,8 +341,6 @@ static void surface_state_move(struct wlr_surface_state *state,
 }
 
 static void surface_apply_damage(struct wlr_surface *surface) {
-	surface->has_buffer = surface->current.buffer;
-
 	if (surface->current.buffer == NULL) {
 		// NULL commit
 		if (surface->buffer != NULL) {
@@ -383,7 +381,7 @@ static void surface_apply_damage(struct wlr_surface *surface) {
 }
 
 static void surface_update_opaque_region(struct wlr_surface *surface) {
-	if (!surface->has_buffer) {
+	if (!wlr_surface_has_buffer(surface)) {
 		pixman_region32_clear(&surface->opaque_region);
 		return;
 	}
@@ -722,7 +720,7 @@ struct wlr_texture *wlr_surface_get_texture(struct wlr_surface *surface) {
 }
 
 bool wlr_surface_has_buffer(struct wlr_surface *surface) {
-	return surface->has_buffer;
+	return surface->current.buffer_width > 0 && surface->current.buffer_height > 0;
 }
 
 void wlr_surface_map(struct wlr_surface *surface) {