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

src/edgeMesh/edgeMesh.C

@@ -123,7 +123,7 @@ Foam::label Foam::edgeMesh::regions(labelList& edgeRegion) const
         edgeRegion[startEdgeI] = currentRegion;
         labelList edgesToVisit(1, startEdgeI);
 
-        while (edgesToVisit.size() > 0)
+        while (edgesToVisit.size())
         {
             // neighbours of current edgesToVisit
             DynamicList<label> newEdgesToVisit(edgesToVisit.size());