Fix weird test failure after c5cd38b

The change in c5cd38b seems like it shouldn't have had any effect,
but creating an empty Set before yielding somehow avoided a race
condition with the subsequent updateSession call.

chrome/content/zotero/xpcom/server_connector.js

@@ -164,17 +164,17 @@ Zotero.Server.Connector.SaveSession.prototype.update = async function (libraryID
 };
 
 Zotero.Server.Connector.SaveSession.prototype._addObjects = async function (objectType, objects) {
-	// Update the objects with the current target data, in case it changed since the save began
-	await this._updateObjects({
-		[objectType]: objects
-	});
-
 	if (!this._objects[objectType]) {
 		this._objects[objectType] = new Set();
 	}
 	for (let object of objects) {
 		this._objects[objectType].add(object);
 	}
+
+	// Update the objects with the current target data, in case it changed since the save began
+	await this._updateObjects({
+		[objectType]: objects
+	});
 };
 
 /**