src/rrd_daemon.c: fix incorrect line number reporting by rrdcached in fetch

src/rrd_daemon.c: fix incorrect line number reporting by rrdcached in fetch

  Example of error:
    rrdtool fetch --daemon 127.0.0.1:42218 <path to>.rrd --start -5min LAST
    ERROR: rrdc_fetch: Got 34 lines, expected 37

  While the same, without '--daemon <address>' works fine.

  The bug manifests itself when the last element of line to write falls
  within the last 10% of the length of 'char linebuf[1024]', ie between
  922 and 1023 bytes; in that case the '\n' at the end of the line is
  not written, and so not seen by count_lines(), wrong number of lines
  given in the daemon's response -> 'rrdtool fetch' errors out.