Image styles not working due to incorrect stream_seek() semantics in stream wrapper.

stream_seek() in PHP stream wrappers should return FALSE on failure and TRUE on success. However the PHP fseek() function returns 0 on success and -1 on failure.

Since HPCloudDrupalStreamWrapper::stream_seek() simply returns the result of fseek(), it will break anytime the stream has to seek, such as when generating derivative images of jpegs with EXIF data in the header. Patch follows.