ALIROOT-5986 ATO-184 - Use the default voltage in case voltage entry …

…for particular chamber not available

ATO-184 - fix in AliTPCcalibDB::GetGainCorrectionHVandPT

ATO-184 Check the pointer before you use it

TPC/Base/AliTPCcalibDB.cxx

@@ -2582,7 +2582,14 @@ Double_t AliTPCcalibDB::GetGainCorrectionHVandPT(Int_t timeStamp, Int_t run, Int
     if (!graphGPT) graphGPT = fParam->GetGainSlopesPT();
     //
     for (Int_t isec=0; isec<72; isec++){
-      Double_t deltaHV= GetChamberHighVoltage(run,isec, timeStamp) - fParam->GetNominalVoltage(isec);
+      Double_t HV= GetChamberHighVoltage(run,isec, timeStamp);
+      if (HV<=0){ // check if the HV was available
+	AliDCSSensor* sensor = GetChamberHVSensor(isec);
+	if (sensor && sensor->GetGraph()==NULL &&  sensor->GetFit()==NULL){
+	  HV=fParam->GetNominalVoltage(isec);
+	}     
+      }
+      Double_t deltaHV= HV - fParam->GetNominalVoltage(isec);
       Double_t deltaGHV=0;
       Double_t deltaGPT=0;
       if (graphGHV) deltaGHV = graphGHV->GetY()[isec]*deltaHV;