Don't block on saving for populating the context.

packages/docregistry/src/context.ts

@@ -186,7 +186,8 @@ class Context<T extends DocumentRegistry.IModel> implements DocumentRegistry.ICo
     if (this._modelDB) {
       return this._modelDB.connected.then(() => {
         if (this._modelDB.isPrepopulated) {
-          return this.save();
+          this.save();
+          return void 0;
         } else {
           return this.revert();
         }