title: Chartboost is not shown more than one time
body: <p>I am new in cocos2dx.Now i add the chartboost in androidstudio.
  But chartboost come only one time then after is not shown permanantly.I call the delegate for log print .
  Log is display below.</p>
  
  <p>Request /interstitial/get succeeded. Response code: 200, body: {"message":"No publisher campaigns found","status":404}</p>
  
  <p>W/network failure﹕ request /interstitial/get failed with error HTTP_NOT_FOUND: 404 error from server</p>
  
  <p>I/Chartboost﹕ DID FAIL TO LOAD INTERSTITIAL 'Default Error: NO_AD_FOUND</p>