title: reCAPTCHA Invisible - reSubmit Form Issue
body: <p>While using reCaptcha, I faced a problem. In code, using AJAX to submit form. Before submitting I need to check if the fields are filled or not. If fields are not filled, submit should not happen.</p>
  
  <p>In this case, if textfields are not filled, it will give an alert. </p>
  
  <p>The problem is after the rejection of invalid post, the submit button stops working for like 2 or 3 minutes and there is no error given by reCaptcha. After the period of time, reCaptcha starts working again and submit button works.</p>
  
  <pre><code>&lt;form id="contact-form" method="post" action="javascript:void(0)"&gt;
         &lt;input type="text" placeholder="Name" id="name"&gt;
         &lt;input type="text" placeholder="E-Mail" id="email"&gt;
         &lt;textarea placeholder="Message" id="message"&gt;/textarea&gt;
         &lt;button class="g-recaptcha pull-right" data-sitekey="#your-site-key" data-callback="sendData" type="submit"&gt; SEND &lt;i class="flaticon-origami34"&gt;&lt;/i&gt; &lt;/button&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>Javascripts : </p>
  
  <pre><code>function sendData(){
  
      console.log('send data - '); // --&gt; works
  
      //send datas: 
  
      $("#contact-form").submit();
  
  };
  
  $('#contact-form').on("submit", function() {
  
  console.log('clicked submit'); // --&gt; works
  
  name = $('#name').val().replace(/&lt;|&gt;/g, ""), // prevent xss
      email = $('#email').val().replace(/&lt;|&gt;/g, ""),
      msg = $('#message').val().replace(/&lt;|&gt;/g, "");
  
  if (name == '' || email == '' || msg == '') {
  
      alert("Please fill all areas !");
  
  } else {
  
      console.log('captcha response: ' + grecaptcha.getResponse()); // --&gt; captcha response: 
  
      // ajax to the php file to send the mail
      $.ajax({
          type: "POST",
          url: "SaveContact.php",
          data: "email=" + email + "&amp;name=" + name + "&amp;msg=" + msg + "&amp;g-recaptcha-response=" + grecaptcha.getResponse()
      }).done(function(status) {
          if (status == "ok") {
              // clear the form fields
              $('#name').val('');
              $('#email').val('');
              $('#message').val('');
          }
      });
  
  }});
  </code></pre>