patch 9.0.1606: using freed memory when 'foldcolumn' is set

Problem:    Using freed memory when 'foldcolumn' is set.
Solution:   Save extra pointer to free it later. (closes #12492)
diff --git a/src/version.c b/src/version.c
index 335e3bd..b17b01b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1606,
+/**/
     1605,
 /**/
     1604,