patch 9.1.1059: completion: input text deleted with preinsert when adding leader

Problem:  completion: input text deleted with preinsert when adding leader
Solution: remove compl_length and check the ptr for being equal
          to pattern when preinsert is active (glepnir)

closes: #16545

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/insexpand.c b/src/insexpand.c
index 63b779d..df757ce 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -4094,7 +4094,7 @@
 	if (!in_fuzzy)
 	    ptr = ins_compl_get_next_word_or_line(st->ins_buf, st->cur_match_pos,
 							       &len, &cont_s_ipos);
-	if (ptr == NULL)
+	if (ptr == NULL || (ins_compl_has_preinsert() && STRCMP(ptr, compl_pattern.string) == 0))
 	    continue;
 
 	if (ins_compl_add_infercase(ptr, len, p_ic,
@@ -4342,7 +4342,7 @@
     int	has_preinsert = ins_compl_preinsert_effect();
     if (has_preinsert)
     {
-	col = compl_col + ins_compl_leader_len() - compl_length;
+	col += ins_compl_leader_len();
 	curwin->w_cursor.col = compl_ins_end_col;
     }