Draft: Avoid null ptr dereference when CALO param histo file not found

Avoids a seg fault due to a null pointer derefence when the param histo file is not found

Error in <TFile::TFile>: file /usera/jonesc/LHCbCMake/Feature/PARAM/ParamFiles/v8r999/data/CaloPID/DLLs_parametrization_histograms.root does not exist
 *** Break *** segmentation violation

instead the application shuts down more gracefully via an exception

Error in <TFile::TFile>: file /usera/jonesc/LHCbCMake/Feature/PARAM/ParamFiles/v8r999/data/CaloPID/DLLs_parametrization_histograms.root does not exist
CaloChargedPIDsAlg_Long               FATAL  Exception with tag=HistoStore is caught 
CaloChargedPIDsAlg_Long               ERROR HistoStore 	 ParamFile '${PARAMFILESROOT}/data/CaloPID/DLLs_parametrization_histograms.root' not found	 StatusCode=FAILURE
HiveDataBrokerSvc                     FATAL in sysInitialize(): exception with tag=instantiateAndInitializeAlgorithms is caught
HiveDataBrokerSvc                     ERROR instantiateAndInitializeAlgorithms 	 Failed to initialize CaloChargedPIDsAlg/CaloChargedPIDsAlg_Long	 StatusCode=FAILURE
ServiceManager                        ERROR Unable to initialize service "HiveDataBrokerSvc"
HLTControlFlowMgr                     FATAL Error retrieving HiveDataBrokerSvc
ServiceManager                        ERROR Unable to initialize Service: HLTControlFlowMgr
ApplicationMgr                        ERROR Application Manager Terminated with error code 1