asset: Add a method to retrieve the GError of an asset loaded with error

API:
    ges_asset_get_error

docs/libs/ges-sections.txt

@@ -1077,6 +1077,7 @@ ges_asset_request
 ges_asset_request_async
 ges_asset_request_finish
 ges_asset_extract
+ges_asset_get_error
 ges_list_assets
 <SUBSECTION Standard>
 GESAssetPrivate

ges/ges-asset.c

@@ -1039,3 +1039,20 @@ ges_list_assets (GType filter)
 
   return ret;
 }
+
+/**
+ * ges_asset_get_error:
+ * @self: The asset to retrieve the error from
+ *
+ * Returns: (transfer none): The #GError of the asset or %NULL if the asset was
+ * loaded without issue
+ *
+ * Since: 1.8
+ */
+GError *
+ges_asset_get_error (GESAsset * self)
+{
+  g_return_val_if_fail (GES_IS_ASSET (self), NULL);
+
+  return self->priv->error;
+}

ges/ges-asset.h

@@ -95,6 +95,7 @@ GESAsset * ges_asset_request         (GType extractable_type,
 const gchar * ges_asset_get_id       (GESAsset* self);
 GESAsset * ges_asset_request_finish  (GAsyncResult *res,
                                       GError **error);
+GError * ges_asset_get_error         (GESAsset * self);
 GESExtractable * ges_asset_extract   (GESAsset * self,
                                       GError **error);
 GList * ges_list_assets              (GType filter);