title: App crashes if PaywithCard is selected in PayPalPaymentViewController [Paypal iOS SDK]
body: <p>I have integrated paypal's payment gate way in my app and I have added all the neccessary sdks and libraries. When I enable <strong>acceptCreditCards</strong> option in paypal configuration, app crashes as soon as user tries to tap on PaywithCard option.</p>
  
  <p>Crash Log:</p>
  
  <pre><code>'Application tried to present a nil modal view controller on target &lt;PayPalPaymentViewController: 0x7fce3029f200
  Environment: sandbox
  languageOrLocale: en-US
  &gt;
  </code></pre>
  
  <p>I even tried enabling PaywithCard in paypal's sample app and observed the same behaviour.I'm using Xcode 8, swift 3 and </p>