in ls.c, should check errno after readdir

In ls.c, errno should be checked after a NULL result from readdir, to see if
there was an error.  It may be that in a "normal" posix system, no error can
happen here, but my NAS box (an EMC Celerra) is reporting EACCES here, so a
defensive check, rather than ignoring the error, would be helpful.

I suppose this applies to all readdir's.

Regards,
Mike



  while ((next = readdir (reading)) != NULL)
    if (file_interesting (next))
      {
	enum filetype type = unknown;

#if HAVE_STRUCT_DIRENT_D_TYPE
	if (next->d_type == DT_DIR || next->d_type == DT_CHR
	    || next->d_type == DT_BLK || next->d_type == DT_SOCK
	    || next->d_type == DT_FIFO)
	  type = next->d_type;
#endif
	total_blocks += gobble_file (next->d_name, type, 0, name);
      }

  if (CLOSEDIR (reading))
    {
      error (0, errno, "%s", quotearg_colon (name));
      exit_status = 1;
      /* Don't return; print whatever we got. */
    }