title: iOS App Crash with [GPUImageContext presentBufferForDisplay]
body: <p>I'm using a GPUImage library for developing an iOS camera app.</p>
  
  <p>I found sometimes app crash with GPUImageContext.
  I noticed it via Crashlytics Crash report, 
  and App crash at GPUImageContext.m line 196, below method.</p>
  
  <pre><code>- (void)presentBufferForDisplay;
  {
      [self.context presentRenderbuffer:GL_RENDERBUFFER];
  }
  </code></pre>
  
  <p>I confirmed below question, but I support below case.<br>
  <a href="https://stackoverflow.com/questions/19379541/mysterious-app-crash-with-opengl">Mysterious app crash with OpenGL</a></p>
  
  <p>Does anyone suggest the reason of this crash?
  I receive crash report, most crash(90%) occur in iPod.</p>