BUG: incorrect bitSet auto-vivify in snappy

- should use bitSet::set() and not bitSet::operator[] to auto-vivify
  out-of-range entries

- use bitSet::test() instead of bitSet::operator[] when testing
  non-const variables - circumvents any potential out-of-range issues.

src/mesh/snappyHexMesh/meshRefinement/meshRefinement.C

@@ -2754,9 +2754,9 @@ const
         label nMasterFaces = 0;
         forAll(isMasterFace, i)
         {
-            if (isMasterFace[i])
+            if (isMasterFace.test(i))
             {
-                nMasterFaces++;
+                ++nMasterFaces;
             }
         }
 
@@ -2764,9 +2764,9 @@ const
         label nMasterPoints = 0;
         forAll(isMeshMasterPoint, i)
         {
-            if (isMeshMasterPoint[i])
+            if (isMeshMasterPoint.test(i))
             {
-                nMasterPoints++;
+                ++nMasterPoints;
             }
         }