score: Add debug support to chains

This helps to detect

 * double insert, append, prepend errors, and
 * get from empty chain errors.

cpukit/sapi/src/rbheap.c

@@ -76,6 +76,7 @@ static void add_to_chain(
   rtems_rbheap_chunk *chunk
 )
 {
+  rtems_chain_initialize_node(&chunk->chain_node);
   rtems_chain_prepend_unprotected(chain, &chunk->chain_node);
 }