BUG: globalSum needed in the merit functions' directional derivative (fixes #1949)

Does not affect the current functionality of shape optimisation.

src/optimisation/adjointOptimisation/adjoint/optimisation/updateMethod/updateMethod/updateMethod.C

@@ -376,7 +376,7 @@ Foam::scalar Foam::updateMethod::computeMeritFunction()
 
 Foam::scalar Foam::updateMethod::meritFunctionDirectionalDerivative()
 {
-    return sum(objectiveDerivatives_*correction_);
+    return globalSum(objectiveDerivatives_*correction_);
 }