patch 8.0.0520: using a function pointer while the function is known

Problem:    Using a function pointer instead of the actual function, which we
            know.
Solution:   Change mb_ functions to utf_ functions when already checked for
            Unicode. (Dominique Pelle, closes #1582)
diff --git a/src/version.c b/src/version.c
index 36adf25..5705d98 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    520,
+/**/
     519,
 /**/
     518,