patch 8.2.4229: possible crash when invoking timer callback fails

Problem:    Possible crash when invoking timer callback fails.
Solution:   Initialize the typval.  Give an error for an empty callback.
            (closes #9636)
diff --git a/src/version.c b/src/version.c
index e3a9715..c8b0ce1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4229,
+/**/
     4228,
 /**/
     4227,