Fix call to fetch favorites on dashboard after database initialization

Scenario to reproduce

1. start Nuxeo against an empty (MongoDB) database
2. Log in
3. Observe the following error in the logs

   2019-03-12 19:26:55,392 WARN  [CoreQueryDocumentPageProvider] Failed to execute query: SELECT * FROM Document where ecm:mixinType != 'HiddenInNavigation' AND ecm:currentLifeCycleState != 'deleted' AND collectionMember:collectionIds/* = ? ORDER BY dc:title, Lexical Error: Illegal character <?> at offset 149
   org.nuxeo.ecm.core.query.QueryParseException: Failed to execute query: SELECT * FROM Document where ecm:mixinType != 'HiddenInNavigation' AND ecm:currentLifeCycleState != 'deleted' AND collectionMember:collectionIds/* = ? ORDER BY dc:title, Lexical Error: Illegal character <?> at offset 149
   	at org.nuxeo.ecm.core.query.sql.parser.Scanner.scanError(Scanner.java:878)
   	at org.nuxeo.ecm.core.query.sql.parser.Scanner.next_token(Scanner.java:1319)
   	at java_cup.runtime.lr_parser.scan(lr_parser.java:335)
   	at java_cup.runtime.lr_parser.parse(lr_parser.java:563)
   	at org.nuxeo.ecm.core.query.sql.SQLQueryParser.parse(SQLQueryParser.java:43)
   	at org.nuxeo.ecm.core.query.sql.SQLQueryParser.parse(SQLQueryParser.java:52)
   	at org.nuxeo.ecm.core.storage.dbs.DBSSession.doQueryAndFetch(DBSSession.java:1501)
   	at org.nuxeo.ecm.core.storage.dbs.DBSSession.doQuery(DBSSession.java:1465)
   	at org.nuxeo.ecm.core.storage.dbs.DBSSession.query(DBSSession.java:1453)
   	at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   	at java.lang.reflect.Method.invoke(Method.java:498)
   	at org.nuxeo.ecm.core.storage.dbs.DBSRepositoryBase$DBSSessionInvoker.invoke(DBSRepositoryBase.java:492)
   	at com.sun.proxy.$Proxy63.query(Unknown Source)
   	at org.nuxeo.ecm.core.api.AbstractSession.query(AbstractSession.java:1182)
   	at org.nuxeo.ecm.core.api.AbstractSession.query(AbstractSession.java:1115)
   	at org.nuxeo.ecm.core.api.AbstractSession.query(AbstractSession.java:1108)
   	at org.nuxeo.ecm.platform.query.nxql.CoreQueryDocumentPageProvider.getCurrentPage(CoreQueryDocumentPageProvider.java:159)
   	at org.nuxeo.ecm.automation.core.util.PaginablePageProvider.<init>(PaginablePageProvider.java:43)
   	at org.nuxeo.ecm.automation.jaxrs.io.documents.PaginableDocumentModelListImpl.<init>(PaginableDocumentModelListImpl.java:49)
   	at org.nuxeo.ecm.restapi.server.jaxrs.search.QueryExecutor.queryByPageProvider(QueryExecutor.java:360)
   	at org.nuxeo.ecm.restapi.server.jaxrs.search.QueryExecutor.queryByPageProvider(QueryExecutor.java:319)
   	at org.nuxeo.ecm.restapi.server.jaxrs.search.SearchObject.doQueryByPageProvider(SearchObject.java:96)
   

This is due to the fact that the call to http://localhost:8080/nuxeo/api/v1/automation/Favorite.Fetch to fetch the favorite container returns an empty response.
The consequence is that this code from nuxeo-home.html

    this._fetchFavorite().then(function (favorite) {
      this.$.favoritesProvider.params = [favorite.uid];
      this.$.favoritesProvider.page = 1;
      this.$.favoriteDocs.fetch();
    }.bind(this)); 

will set an empty parameter for favorite.uid, hence the error.