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/mesh/manipulation/createPatch/createPatch.C

@@ -172,7 +172,7 @@ void filterPatches(polyMesh& mesh)
 
         if (isA<processorPolyPatch>(pp))
         {
-            if (pp.size() > 0)
+            if (pp.size())
             {
                 allPatches.append
                 (
@@ -586,7 +586,7 @@ int main(int argc, char *argv[])
     // 1. Add all new patches
     // ~~~~~~~~~~~~~~~~~~~~~~
 
-    if (patchSources.size() > 0)
+    if (patchSources.size())
     {
         // Old and new patches.
         DynamicList<polyPatch*> allPatches(patches.size()+patchSources.size());