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)

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3721,
 /**/
     3720,
 /**/