patch 9.1.0172: More code can use ml_get_buf_len() instead of STRLEN()

Problem:  More code can use ml_get_buf_len() instead of STRLEN().
Solution: Change more STRLEN() calls to ml_get_buf_len().  Also do not
          set ml_line_textlen in ml_replace_len() if "has_props" is set,
          because "len_arg" also includes the size of text properties in
          that case. (zeertzjq)

closes: #14183

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/help.c b/src/help.c
index c33985e..a792bf3 100644
--- a/src/help.c
+++ b/src/help.c
@@ -720,7 +720,7 @@
 	for (lnum = 1; lnum <= curbuf->b_ml.ml_line_count; ++lnum)
 	{
 	    line = ml_get_buf(curbuf, lnum, FALSE);
-	    len = (int)STRLEN(line);
+	    len = ml_get_buf_len(curbuf, lnum);
 	    if (in_example && len > 0 && !VIM_ISWHITE(line[0]))
 	    {
 		// End of example: non-white or '<' in first column.