patch 8.2.1373: Vim9: no error for assigning to non-existing script var

Problem:    Vim9: no error for assigning to non-existing script var.
Solution:   Check that in Vim9 script the variable was defined. (closes #6630)
diff --git a/src/structs.h b/src/structs.h
index 7e34d80..a80de6a 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1594,7 +1594,9 @@
     int		uf_tml_execed;	// line being timed was executed
 # endif
     sctx_T	uf_script_ctx;	// SCTX where function was defined,
-				// used for s: variables
+				// used for s: variables; sc_version changed
+				// for :function
+    int		uf_script_ctx_version;  // original sc_version of SCTX
     int		uf_refcount;	// reference count, see func_name_refcount()
 
     funccall_T	*uf_scoped;	// l: local variables for closure