patch 8.2.3218: when using xchaha20 crypt undo file is not removed

Problem:    When using xchaha20 crypt undo file is not removed.
Solution:   Reset 'undofile' and delete the file. (Christian Brabandt,
            closes #8630, closes #8467)
diff --git a/src/version.c b/src/version.c
index 9e77d56..9b334e6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3218,
+/**/
     3217,
 /**/
     3216,