title: App crashes after send button in Mail Composer is pressed
body: <p>I have a mailHelper class like following:</p>
  
  <pre><code>class MailHelper: NSObject, MFMailComposeViewControllerDelegate {
      //MARK: Mail Function
      func configuredInquiryMailComposeViewController(rootViewController: UIViewController) {
          let mailComposerVC = MFMailComposeViewController()
          mailComposerVC.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.whiteColor(), NSFontAttributeName: UIFont(name: "AvenirNext-Medium", size: 20)!]
          mailComposerVC.navigationBar.tintColor = UIColor.whiteColor()
          mailComposerVC.navigationBar.translucent = false
          mailComposerVC.mailComposeDelegate = self
          mailComposerVC.setToRecipients(["(email)"])
          mailComposerVC.setSubject("(title)")
          mailComposerVC.setMessageBody("[Please write your inquiries below. We will reply shortly]", isHTML: false)
  
          if MFMailComposeViewController.canSendMail() {
              rootViewController.presentViewController(mailComposerVC, animated: true, completion: nil)
          } else {
                              showSendMailErrorAlert()
          }
      }
  
      func showSendMailErrorAlert() {
          let sendMailErrorAlert = UIAlertController(title: "Could Not Send Email", message: "Your device could not send e-mail.  Please check e-mail configuration and try again.", preferredStyle: UIAlertControllerStyle.Alert)
          let cancelAction: UIAlertAction = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)
          sendMailErrorAlert.addAction(cancelAction)
          self.presentViewController(sendMailErrorAlert, animated: true, completion: nil)
      }
  
      // MARK: MFMailComposeViewControllerDelegate Method
      func mailComposeController(controller: MFMailComposeViewController, didFinishWithResult result: MFMailComposeResult, error: NSError?) {
          controller.dismissViewControllerAnimated(true, completion: nil)
      }
  
  }
  </code></pre>
  
  <p>Then I call this helper function in my main view controller:</p>
  
  <pre><code>override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
      if (indexPath.section == 0 &amp;&amp; indexPath.row == 0) {
                  let mailHelperClass = MailHelper()
                 mailHelperClass.configuredInquiryMailComposeViewController(self)
              }
  }
  </code></pre>
  
  <p>When I click the cell in tableview in main view controller, Mail Composer is successfully shown. The problem is that whenever I click "Send" or "Cancel" button in the mail composer, it crashes the app. </p>
  
  <p>To make sure whether this helper class is wrong, I got rid of the helper class and migrated all mail composer related functions into my main view controller. Then, it worked whenever I clicked "Send" or "Cancel" button. What am I doing wrong in my <code>mail helper class</code>?</p>
  
  <p>When it crashes, it does not give me any error message.</p>