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/postProcessing/graphics/ensightFoamReader/USERD_set_filenames.H

@@ -147,14 +147,14 @@ int USERD_set_filenames
     
     bool lagrangianNamesFound = false;
     label n = 0;
-    while ((!lagrangianNamesFound) && (n<Num_time_steps))
+    while (!lagrangianNamesFound && n < Num_time_steps)
     {
         runTime.setTime(TimeList[n+1], n+1);
 
         Cloud<passiveParticle> lagrangian(*meshPtr);
 
         n++;
-        if (lagrangian.size()>0)
+        if (lagrangian.size())
         {
             lagrangianNamesFound = true;
         }