decompositionMethod::scaleWeights: Only call reduce if running distributed

src/parallel/decompose/decompositionMethods/decompositionMethod/decompositionMethod.C

@@ -306,7 +306,11 @@ Foam::labelList Foam::decompositionMethod::scaleWeights
         {
             sumIntWeights[i % nWeights] += intWeights[i];
         }
+
+        if (distributed)
+        {
             reduce(sumIntWeights, ListOp<sumOp<label>>());
+        }
 
         // Check that the sum of each weight is non-zero
         boolList nonZeroWeights(nWeights, false);