patch 8.2.3380: crash when using NULL string for funcref()

Problem:    Crash when using NULL string for funcref().
Solution:   Check for NULL argument. (issue #8260)
diff --git a/src/version.c b/src/version.c
index c2e07c6..e9a04e2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3380,
+/**/
     3379,
 /**/
     3378,