patch 8.2.4417: using NULL pointer

Problem:    Using NULL pointer.
Solution:   Set offset after checking for NULL pointer.
diff --git a/src/userfunc.c b/src/userfunc.c
index 696320c..3e0d021 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -4024,7 +4024,7 @@
 get_scriptlocal_funcname(char_u *funcname)
 {
     char	sid_buf[25];
-    int		off = *funcname == 's' ? 2 : 5;
+    int		off;
     char_u	*newname;
     char_u	*p = funcname;
 
@@ -4047,6 +4047,8 @@
 	++p;
 	off = 0;
     }
+    else
+	off = *funcname == 's' ? 2 : 5;
 
     if (!SCRIPT_ID_VALID(current_sctx.sc_sid))
     {