BradLarson/GPUImage — pull request #492 by brettg (2012-09-21 22:49:17+00:00)
Title: prevent crash when captureStillImageAsynchronouslyFromConnection yields an error

If ```captureStillImageAsynchronouslyFromConnection``` calls back with an error in any of the capture methods of ```GPUImageStillCamera``` a crash occurs when ```imageSampleBuffer```, now == ```NULL``` eventually gets passed to ```CFRetain```.

The change in this pull request checks if ```imageSampleBuffer``` is ```NULL``` and if so bails out of the methods accordingly.