Code review comment for lp:~laurynas-biveinis/percona-server/merge-5.6.16

A merge regression in that buf_flush_page_and_try_neighbors() will return an uninitialized value if doing flush list flushing and encountering a page not ready for flush:

...
 ibool flushed;
...
 if (buf_flush_ready_for_flush(bpage, flush_type)) {
...
  flushed = TRUE;
 } else if (flush_type == BUF_FLUSH_LRU) {
...
  flushed = FALSE;
 }
...
 return(flushed);