fix(lua): make vim.str_utfindex and vim.str_byteindex handle NUL bytes

fixes #16290

2 files changed, 5 insertions, 4 deletions

diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index 310ad05196..ac3fbe9acd 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1457,7 +1457,7 @@ void mb_utflen(const char_u *s, size_t len, size_t *codepoints, size_t *codeunit
 {
   size_t count = 0, extra = 0;
   size_t clen;
-  for (size_t i = 0; i < len && s[i] != NUL; i += clen) {
+  for (size_t i = 0; i < len; i += clen) {
     clen = (size_t)utf_ptr2len_len(s + i, (int)(len - i));
     // NB: gets the byte value of invalid sequence bytes.
     // we only care whether the char fits in the BMP or not
@@ -1479,7 +1479,7 @@ ssize_t mb_utf_index_to_bytes(const char_u *s, size_t len, size_t index, bool us
   if (index == 0) {
     return 0;
   }
-  for (i = 0; i < len && s[i] != NUL; i += clen) {
+  for (i = 0; i < len; i += clen) {
     clen = (size_t)utf_ptr2len_len(s + i, (int)(len - i));
     // NB: gets the byte value of invalid sequence bytes.
     // we only care whether the char fits in the BMP or not
diff --git a/src/nvim/memline.c b/src/nvim/memline.c
index 9d1ad5903d..c1c3308118 100644
--- a/src/nvim/memline.c
+++ b/src/nvim/memline.c
@@ -2296,8 +2296,9 @@ void ml_add_deleted_len_buf(buf_T *buf, char_u *ptr, ssize_t len)
   if (inhibit_delete_count) {
     return;
   }
-  if (len == -1) {
-    len = (ssize_t)STRLEN(ptr);
+  ssize_t maxlen = (ssize_t)STRLEN(ptr);
+  if (len == -1 || len > maxlen) {
+    len = maxlen;
   }
   curbuf->deleted_bytes += (size_t)len + 1;
   curbuf->deleted_bytes2 += (size_t)len + 1;