title: check if property exists in dynamic jObject
body: <p>so I have a string containing a json</p>
  
  <pre><code>dynamic jsonQuery = JObject.Parse(query);
  </code></pre>
  
  <p>since this object I don't always get all the property's I need to be able to check if a ceratin property exits</p>
  
  <pre><code>if (IsProperty(jsonQuery,"MetaContent"))
  {
    // do stuff
  }
  </code></pre>
  
  <p>I tried it with  classic reflection but that does not seem to work:</p>
  
  <pre><code>private bool IsProperty(object obj, string propertyName)
  {
      return obj.GetType().GetProperty(propertyName) != null;
  }
  </code></pre>
  
  <p>The function always returns <code>false</code> any idea?</p>