Data binding causes infinite loop if value is NaN

[arodic]

Steps to reproduce:

1. Create two elements and bind some property.
2. Make value NaN
3. Notice error: Uncaught RangeError: Maximum call stack size exceeded.

Below is some sample code that returns error when parent-el is instantiated.

<dom-module id="child-el">
  <template>{{value}}</template>
</dom-module>
<script>
(function() {
  Polymer({
    is: 'child-el',
    properties: {
      value: {
        value: null,
        notify: true
      }
    }
  });
}());
</script>

<dom-module id="parent-el">
  <template><child-el value="{{numvalue}}"></child-el></template>
</dom-module>
<script>
(function() {
  Polymer({
    is: 'parent-el',
    properties: {
      numvalue: {
        value: NaN,
        notify: true
      }
    }
  });
}());
</script>