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/parallelProcessing/decomposePar/distributeCells.C

@@ -104,7 +104,7 @@ void domainDecomposition::distributeCells()
         }
     }
 
-    if (sameProcFaces.size() > 0)
+    if (sameProcFaces.size())
     {
         Info<< "Selected " << sameProcFaces.size()
             << " faces whose owner and neighbour cell should be kept on the"
@@ -123,7 +123,7 @@ void domainDecomposition::distributeCells()
         *this
     );
 
-    if (sameProcFaces.size() == 0)
+    if (sameProcFaces.empty())
     {
         cellToProc_ = decomposePtr().decompose(cellCentres());
     }