patch 8.2.4453: :helpgrep may free an option that was not allocated

Problem:    :helpgrep may free an option that was not allocated. (Yegappan
            Lakshmanan)
Solution:   Check if the value was allocated.
diff --git a/src/version.c b/src/version.c
index 1786ceb..57f32cb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4453,
+/**/
     4452,
 /**/
     4451,