Fix GCC maybe-uninitialized warning

analytics/operators/aggregator/AggregatorOperator.cpp

@@ -92,6 +92,8 @@ void AggregatorOperator::compute_internal(U_Ptr unit, vector<reading_t> *buffer)
                     reading.value = computeObs(_buffer);
                     break;
                 default:
+                    LOG(warning) << _name << ": Encountered unknown operation!";
+                    reading.value = 0;
                     break;
             }
             out->storeReading(reading);