patch 8.2.3381: crash when using NULL list with sign functions

Problem:    Crash when using NULL list with sign functions.
Solution:   Handle a NULL list like an empty list. (issue #8260)
diff --git a/src/version.c b/src/version.c
index e9a04e2..1fffa73 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3381,
+/**/
     3380,
 /**/
     3379,