[BUGFIX] ConfigurationManager resolves bad PID from TS root record

This fixes a problem where page UID would be zero when Flux's overridden BackendConfigurationManager encountered cases where root page UID had to be resolved from an existing root TS record (as per default Extbase behavior - e.g. "use PID of primary root TS template"). Due to missing the `pid` field in query to select this TS record, the page UID would become zero (integer cast of a NULL value).

Problem was primarily present in backend modules based on Extbase and which do NOT use the page tree.