[turbofan] Only consider inhabited types for constant folding in typed lowering.

test/mjsunit/compiler/regress-621423.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --allow-natives-syntax
 
-Array.prototype.__proto__ = null;
-var prototype = Array.prototype;
+var a = [0, ""];
+a[0] = 0;
+
+function g(array) {
+  array[1] = undefined;
+}
+
 function f() {
-  prototype.lastIndexOf({});
+  g(function() {});
+  g(a);
 }
-f();
+
 f();
 %OptimizeFunctionOnNextCall(f);
 f();