Add some const qualifier

No functional change.

src/search.cpp

@@ -1552,7 +1552,7 @@ void Thread::idle_loop() {
           if (Threads.size() > 2)
               for (size_t i = 0; i < Threads.size(); ++i)
               {
-                  int size = Threads[i]->splitPointsSize; // Local copy
+                  const int size = Threads[i]->splitPointsSize; // Local copy
                   sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
 
                   if (   sp

src/thread.cpp

@@ -119,7 +119,7 @@ bool Thread::available_to(const Thread* master) const {
 
   // Make a local copy to be sure it doesn't become zero under our feet while
   // testing next condition and so leading to an out of bounds access.
-  int size = splitPointsSize;
+  const int size = splitPointsSize;
 
   // No split points means that the thread is available as a slave for any
   // other thread otherwise apply the "helpful master" concept if possible.