BUG: parallel foamToEnsight fails depending on lagrangian order (fixes #1873)

- the problem arises when output fields are missing on some
  processors.

  When the information is combined, the resulting HashTables can have
  different insertion orders. This poses an issue when there are hash
  key collisions and thus different chaining.

- Use sorted order.

applications/utilities/postProcessing/dataConversion/foamToEnsight/convertLagrangian.H

@@ -71,10 +71,10 @@ if (doLagrangian)
             }
         }
 
-        forAllConstIters(theseCloudFields, fieldIter)
+        // Field order may differ on individual processors, so sort by name
+        for (const word& fieldName : theseCloudFields.sortedToc())
         {
-            const word& fieldName = fieldIter.key();
-            const word& fieldType = fieldIter.object();
+            const word& fieldType = theseCloudFields[fieldName];
 
             IOobject fieldObject
             (
@@ -92,9 +92,13 @@ if (doLagrangian)
                 // but that combination does not work.
                 // So check the header and sync globally
 
+                const bool parRun = Pstream::parRun();
+                Pstream::parRun() = false;
+
                 fieldExists =
                     fieldObject.typeHeaderOk<IOField<scalar>>(false);
 
+                Pstream::parRun() = parRun;
                 reduce(fieldExists, orOp<bool>());
             }