wayland: only unset image description if we couldn't set a new one

set_image_description replaces the old image description, so we don't
need to call unset_image_description unconditionally. Only call it if we
couldn't set an image description.

This helps with the lack of synchronization between VO pageflips and
wayland protocol events mentioned in the previous commit.

Author: llyyr

video/out/wayland_common.c

@@ -2108,6 +2108,7 @@ static void image_description_failed(void *data, struct wp_image_description_v1
 {
     struct vo_wayland_state *wl = data;
     MP_VERBOSE(wl, "Image description failed: %d, %s\n", cause, msg);
+    wp_color_management_surface_v1_unset_image_description(wl->color_surface);
     wp_image_description_v1_destroy(image_description);
 }
 
@@ -3450,17 +3451,17 @@ static void set_color_management(struct vo_wayland_state *wl)
     if (!wl->color_surface)
         return;
 
-    wp_color_management_surface_v1_unset_image_description(wl->color_surface);
-
     struct pl_color_space color = wl->target_params.color;
     int primaries = wl->primaries_map[color.primaries];
     int transfer = wl->transfer_map[color.transfer];
     if (!primaries)
         MP_VERBOSE(wl, "Compositor does not support color primary: %s\n", m_opt_choice_str(pl_csp_prim_names, color.primaries));
     if (!transfer)
         MP_VERBOSE(wl, "Compositor does not support transfer function: %s\n", m_opt_choice_str(pl_csp_trc_names, color.transfer));
-    if (!primaries || !transfer)
+    if (!primaries || !transfer) {
+        wp_color_management_surface_v1_unset_image_description(wl->color_surface);
         return;
+    }
 
     struct wp_image_description_creator_params_v1 *image_creator_params =
         wp_color_manager_v1_create_parametric_creator(wl->color_manager);