Simplify checking of container (List/HashTable, strings) sizes

- can use 'XX.empty()' instead of 'XX.size() == 0', 'XX.size() < 1' or
  'XX.size() <= 0' or for simpler coding.
  It also has the same number of characters as '!XX.size()' and /might/ be
  more readable

- many size checking had 'XX.size() > 0', 'XX.size() != 0', or 'XX.size() >= 1'
  when a simple 'XX.size()' suffices

applications/utilities/mesh/generation/blockMesh/blockMesh.C

@@ -118,7 +118,7 @@ Foam::label Foam::blockMesh::numZonedBlocks() const
 
     forAll(*this, blockI)
     {
-        if (operator[](blockI).blockDef().zoneName().size() > 0)
+        if (operator[](blockI).blockDef().zoneName().size())
         {
             num++;
         }

applications/utilities/mesh/generation/blockMesh/blockMeshApp.C

@@ -278,7 +278,7 @@ int main(int argc, char *argv[])
             const labelListList& blockCells = b.cells();
             const word& zoneName = b.blockDef().zoneName();
 
-            if (zoneName.size() > 0)
+            if (zoneName.size())
             {
                 HashTable<label>::const_iterator iter = zoneMap.find(zoneName);
 

applications/utilities/mesh/generation/blockMesh/mergePatchPairs.C

@@ -1,6 +1,6 @@
         Info<< "Creating merge patch pairs" << nl << endl;
 
-        if (mergePatchPairs.size() > 0)
+        if (mergePatchPairs.size())
         {
             // Create and add point and face zones and mesh modifiers
             List<pointZone*> pz(mergePatchPairs.size());