(adjust_markers_for_insert): Adjust markers by taking

(adjust_markers_for_insert): Adjust markers by taking
combined_before_bytes and combined_after_bytes into account.
(count_combining_after): Handle the case that LENGTH is zero.
(adjust_after_replace): Record deletion at correct buffer
position.  Handle the case that LEN is zero.
(replace_range): Record deletion at correct buffer position.
(del_range_2): Call adjust_makers_for_replace to adjust makers for
combined bytes.