encoder_example: exit if encoder wasn't allocated
encoder_example: exit if encoder wasn't allocated

Also avoids leaking ogg_stream.

xiph/daala,ycho/daala,luctrudeau/daala,luctrudeau/daala,xiph/daala,xiph/daala,ycho/daala,ycho/daala,luctrudeau/daala,xiph/daala,luctrudeau/daala,ycho/daala,luctrudeau/daala,ycho/daala,xiph/daala