count characters if possible (if count would move past the
start or end of the buffer, moves to the start or end of the
buffer). The return value indicates whether the new position of
iter is different from its original position, and dereferenceable
(the last iterator in the buffer is not dereferenceable). If count
is 0, the function does nothing and returns FALSE.gtkTextIterForwardChars(object, count)objectcountiter moved and is dereferenceable