GR-9814: fix lambda def arglist parsing when no args are specified

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/ScopeTranslator.java

@@ -155,7 +155,9 @@ public T visitLambdef_nocond_body(Python3Parser.Lambdef_nocond_bodyContext ctx)
     @Override
     public T visitLambdef(Python3Parser.LambdefContext ctx) {
         argListCompilers.push(new ArgListCompiler<>(core));
-        ctx.accept(argListCompilers.peek());
+        if (ctx.varargslist() != null) {
+            ctx.accept(argListCompilers.peek());
+        }
         environment.beginScope(ctx, ScopeKind.Function);
         try {
             return super.visitLambdef(ctx);