Fixes number of entries in ROOT histograms created by RootSink

This number was wrongly computed by ROOT and needed to be overwritten manually. This bit was missing in the original Sink.

GaudiCommonSvc/src/HistogramPersistencySvc/RootHistogramSink.cpp

@@ -54,6 +54,7 @@ namespace {
     auto axis     = std::array{toAxis( jsonAxis[index] )...};
     auto weights  = j.at( "bins" ).get<std::vector<typename Traits::WeightType>>();
     auto title    = j.at( "title" ).get<std::string>();
+    auto nentries = j.at( "nEntries" ).get<unsigned int>();
     // weird way ROOT has to give titles to axis
     title += ( axis[index].title + ... );
     // compute total number of bins, multiplying bins per axis
@@ -126,6 +127,8 @@ namespace {
       }
     };
     ( try_set_bin_labels( index ), ... );
+    // Fix the number of entries, wrongly computed by ROOT from the numer of calls to fill
+    histo.SetEntries( nentries );
     // write to file
     histo.Write();