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/meshTools/triSurface/booleanOps/surfaceIntersection/surfaceIntersectionFuncs.C

@@ -291,7 +291,7 @@ void Foam::surfaceIntersection::writeIntersectedEdges
     {
         const labelList& extraVerts = edgeCutVerts[edgeI];
 
-        if (extraVerts.size() != 0)
+        if (extraVerts.size())
         {
             const edge& e = surf.edges()[edgeI];