[turbofan] Fix control reducer for degenerate cases of self-loop branches.

test/mjsunit/regress/regress-447526.js

 // Copyright 2014 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
 
-function foo() {
-  var a = {b: -1.5};
-  for (var i = 0; i < 1; i++) {
-    a.b = 1;
-  }
-  assertTrue(0 <= a.b);
+function bar() {
+  throw "done";
 }
 
-foo();
-foo();
+function foo() {
+  var i;
+  while (i) {
+    while (i) {
+}
+    i++;
+  }
+  while (true) {
+    bar();
+  }
+}
+
+
 %OptimizeFunctionOnNextCall(foo);
-foo();
+assertThrows(foo);