Otherwise a frame with non-zero nb_samples but without any data can be
returned.
Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
(cherry picked from commit 42e7a5b3c7)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>