patch 9.1.0021: i_CTRL-R- doesn't work for multibyte chars in Replace mode

Problem:  i_CTRL-R- doesn't work for multibyte chars in Replace mode,
          Coverity complains missing return value for u_save_cursor()
Solution: Use mb_charlen() and del_chars() instead, handle failure mode
          for u_save_cursor() correctly (@zeertzjq)

closes: #13846

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 76a7668..b221faa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    21,
+/**/
     20,
 /**/
     19,