patch 8.2.1531: Vim9: test still fails on MS-Windows

Problem:    Vim9: test still fails on MS-Windows.
Solution:   When skipping expect function to be NULL.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index c9805f6..5e4bfdb 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -4271,7 +4271,7 @@
     ufunc = def_function(eap, lambda_name);
 
     if (ufunc == NULL)
-	return NULL;
+	return eap->skip ? (char_u *)"" : NULL;
     if (ufunc->uf_def_status == UF_TO_BE_COMPILED
 	    && compile_def_function(ufunc, TRUE, cctx) == FAIL)
 	return NULL;