patch 8.0.0518: bad fold text when a multi-byte char has a zero byte

Problem:    Storing a zero byte from a multi-byte character causes fold text
            to show up wrong.
Solution:   Avoid putting zero in ScreenLines. (Christian Brabandt,
            closes #1567)
diff --git a/src/version.c b/src/version.c
index 1afe3ab..45d6e8f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    518,
+/**/
     517,
 /**/
     516,