Simplify as suggested by Havoc. Just get the last iter and work backward

Simplify as suggested by Havoc. Just get the last iter and work backward

2001-05-22  Joe Shaw  <joe@ximian.com>

	* gtk/gtktextiter.c (_gtk_text_btree_get_iter_at_last_toggle):
	Simplify as suggested by Havoc. Just get the last iter and work
	backward to the tag instead of getting a line and working back from
	there. Fixes passing in an invalid offset to
	iter_init_from_byte_offset().