patch 8.2.3721: using memory freed by losing the clipboard selection

Problem:    Using memory freed by losing the clipboard selection. (Dominique
            Pellé)
Solution:   Check y_array is still valid after calling changed_lines().
            (closes #9253)
diff --git a/src/version.c b/src/version.c
index 810567f..30cd9bc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3721,
+/**/
     3720,
 /**/
     3719,