iDQ: FIX. Check that there are times available for ifo before requesting values of idq timeseries

Previous commit checked that ifo was available in the history, but NearestLeafTree objects are created for ifos based on whether the analysis is analyzing htem and not whether idq channels were provided for them. Fix it so that here it checks if any times have been stored for that ifo before attempting to request the corresponding idq timeseries value.