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/surfaceIntersection.C

@@ -1044,7 +1044,7 @@ Foam::surfaceIntersection::surfaceIntersection
     transfer(allCutPoints, cutPoints_);
 
     // Shortcut. 
-    if ((cutPoints_.size() == 0) && (cutEdges_.size() == 0))
+    if (cutPoints_.empty() && cutEdges_.empty())
     {
         if (debug)
         {