patch 8.1.1007: using closure may consume a lot of memory

Problem:    Using closure may consume a lot of memory.
Solution:   unreference items that are no longer needed. Add a test. (Ozaki
            Kiichi, closes #3961)
diff --git a/src/version.c b/src/version.c
index 054066e..fb39cf5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -780,6 +780,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1007,
+/**/
     1006,
 /**/
     1005,