BUG: redistributePar fails with some area fields (fixes #2574)

- this is especially evident in -reconstruct mode when
  the fields have several processor boundaries.

  Testing for an existing patch edge mapping must use the `test`
  method (with range-checking) instead of the more common `set`
  method since the source field will likely have many more boundaries
  than physical edge mappings.

src/finiteArea/distributed/faMeshDistributorTemplates.C

@@ -93,7 +93,7 @@ Foam::faMeshDistributor::distributeField
 
     forAll(bfld, patchi)
     {
-        if (patchEdgeMaps_.set(patchi))
+        if (patchEdgeMaps_.test(patchi))
         {
             // Clone local patch field
 
@@ -203,7 +203,7 @@ Foam::faMeshDistributor::distributeField
 
     forAll(bfld, patchi)
     {
-        if (patchEdgeMaps_.set(patchi))
+        if (patchEdgeMaps_.test(patchi))
         {
             // Clone local patch field