patch 7.4.1421
Problem:    May free a channel when a callback may need to be invoked.
Solution:   Keep the channel when refcount is zero.
diff --git a/src/version.c b/src/version.c
index de20c3e..4220001 100644
--- a/src/version.c
+++ b/src/version.c
@@ -749,6 +749,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1421,
+/**/
     1420,
 /**/
     1419,