updated for version 7.4.323
Problem:    Substitute() with zero width pattern breaks multi-byte character.
Solution:   Take multi-byte character size into account. (Yukihiro Nakadaira)
diff --git a/src/testdir/test69.ok b/src/testdir/test69.ok
index 41cd9d0..af8befb 100644
--- a/src/testdir/test69.ok
+++ b/src/testdir/test69.ok
@@ -160,3 +160,7 @@
 [0, 1, 3, 4, -1]
 [0, 1, 2, 4, 5, -1]
 
+
+substitute
+a1a2a3a
+