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/fieldview9Reader/fieldview9Reader.C

@@ -235,7 +235,7 @@ static void createFieldNames
     HashSet<word> surfScalarHash;
     HashSet<word> surfVectorHash;
 
-    if (setName.size() == 0)
+    if (setName.empty())
     {
         forAll(Times, timeI)
         {
@@ -536,13 +536,12 @@ void user_query_file_function
     fileName caseName(rootAndCase.name());
 
     // handle trailing '/'
-    if (caseName.size() == 0)
+    if (caseName.empty())
     {
         caseName = rootDir.name();
-        rootDir = rootDir.path();
+        rootDir  = rootDir.path();
     }
 
-
     Info<< "rootDir  : " << rootDir << endl
         << "caseName : " << caseName << endl
         << "setName  : " << setName << endl;