fix CalcStat on empty operations list

AsbCloudInfrastructure/Services/WellOperationsStatService.cs

@@ -195,11 +195,15 @@ namespace AsbCloudInfrastructure.Services
                 .Where(o => o.IdWellSectionType == idSectionType)
                 .OrderBy(o => o.Start)
                 .ThenBy(o => o.WellDepth);
+            
             return CalcStat(sectionOperations);
         }
 
         private static StatOperationsDto CalcStat(IEnumerable<OperationParams> operations)
         {
+            if (!operations.Any())
+                return null;
+
             var races = GetCompleteRaces(operations);
 
             var section = new StatOperationsDto