patch 8.1.0515: reloading a script gives errors for existing functions

Problem:    Reloading a script gives errors for existing functions.
Solution:   Allow redefining a function once when reloading a script.
diff --git a/src/globals.h b/src/globals.h
index 511479d..131c13b 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -326,7 +326,7 @@
 EXTERN int	garbage_collect_at_exit INIT(= FALSE);
 
 // Script CTX being sourced or was sourced to define the current function.
-EXTERN sctx_T	current_sctx INIT(= {0 COMMA 0});
+EXTERN sctx_T	current_sctx INIT(= {0 COMMA 0 COMMA 0});
 #endif
 
 EXTERN int	did_source_packages INIT(= FALSE);