patch 9.0.1609: crash when an object indirectly references itself

Problem:    Crash when an object indirectly references itself.
Solution:   Avoid clearing an object while it is already being cleared.
            (closes #12494)
diff --git a/src/version.c b/src/version.c
index 1a8dd0e..1288490 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1609,
+/**/
     1608,
 /**/
     1607,