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/splitMeshRegions/splitMeshRegions.C

@@ -878,7 +878,7 @@ void createAndWriteRegion
     {
         const polyPatch& pp = newPatches[patchI];
 
-        if (isA<processorPolyPatch>(pp) && pp.size() > 0)
+        if (isA<processorPolyPatch>(pp) && pp.size())
         {
             oldToNew[patchI] = newI++;
         }
@@ -1049,7 +1049,7 @@ label findCorrespondingZone
 
     labelList regionCells = findIndices(cellRegion, regionI);
 
-    if (regionCells.size() == 0)
+    if (regionCells.empty())
     {
         // My local portion is empty. Maps to any empty cellZone. Mark with
         // special value which can get overwritten by other processors.
@@ -1200,7 +1200,7 @@ int main(int argc, char *argv[])
     boolList blockedFace;
 
     // Read from faceSet
-    if (blockedFacesName.size() > 0)
+    if (blockedFacesName.size())
     {
         faceSet blockedFaceSet(mesh, blockedFacesName);
         Info<< "Read " << returnReduce(blockedFaceSet.size(), sumOp<label>())