miv authored Jul 14, 2017 and Jean-Marc Valin committed Jul 25, 2017

ope_encoder_create_pull calls ope_encoder_create_callbacks with a
NULL callbacks argument, which causes the function to crash. Test
for NULL to prevent this.

As well, we try and call the close callback when flushing the stream,
which also leads to a crash when the callbacks are not set. Don't call
the callback in pull mode.

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>