When evictableMmapped or evictable size is zero, do not throw NoSuchElementException

  /**
   * Trim the eviction lists.
   */
  private void trimEvictionMaps() {
    long now = Time.monotonicNow();
    demoteOldEvictableMmaped(now);

    while (true) {
      long evictableSize = evictable.size();
      long evictableMmappedSize = evictableMmapped.size();
      if (evictableSize + evictableMmappedSize <= maxTotalSize) {
        return;
      }
      ShortCircuitReplica replica;
      try {
        if (evictableSize == 0) {
          replica = (ShortCircuitReplica)evictableMmapped.get(evictableMmapped
              .firstKey());
        } else {
          replica = (ShortCircuitReplica)evictable.get(evictable.firstKey());
        }
      } catch (NoSuchElementException e) {
        break;
      }
      if (LOG.isTraceEnabled()) {
        LOG.trace(this + ": trimEvictionMaps is purging " + replica +
            StringUtils.getStackTrace(Thread.currentThread()));
      }
      purge(replica);
    }
  }