MetaReaderPeeker: Select first file with events for metadata peeking ATEAM-757

While working on allowing the CutFlowSvc to handle event-less files in !44993 (merged) we realized that the autoconfiguration is broken when the first file in the input list contains no events. This MR addresses this by having the metadata peeker deliver the information from the first input file with events.

Much of the information the autoconfiguration grabs from file metadata requires at least one event to have been written by the stream that produced the file. To ensure those values are present in the metadata supplied to the autoconfiguration by the peeker select use the first input file with at least one event.