patch 9.0.1914: Vim9: few issues when accessing object members

Problem:  Vim9: few issues when accessing object members
Solution: When calling an object method, check for null object.
          Accessing a Dict object member doesn't work.

closes: #13119
closes: #13123
closes: #13124

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index 3f44b88..0ca3be1 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -2617,7 +2617,7 @@
 	    return NULL;
 	}
 
-	if (cctx->ctx_ufunc->uf_flags & FC_NEW)
+	if (IS_CONSTRUCTOR_METHOD(cctx->ctx_ufunc))
 	{
 	    // For a class new() constructor, return an object of the class.
 	    generate_instr(cctx, ISN_RETURN_OBJECT);