patch 9.1.0168: too many STRLEN() calls

Problem:  too many STRLEN() calls
Solution: Make use of ml_get_len() calls instead
          (John Marriott)

closes: #14123

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/memline.c b/src/memline.c
index 99b9e9f..5228155 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -3661,7 +3661,7 @@
 
     curbuf->b_ml.ml_line_ptr = line;
     curbuf->b_ml.ml_line_len = len;
-    curbuf->b_ml.ml_line_textlen = len_arg + 1;
+    curbuf->b_ml.ml_line_textlen = len_arg + !has_props;
     curbuf->b_ml.ml_line_lnum = lnum;
     curbuf->b_ml.ml_flags = (curbuf->b_ml.ml_flags | ML_LINE_DIRTY) & ~ML_EMPTY;