vorbis_analysis_headerout calls oggpack_writeclear with uninitialized ogb if !v->backend_state
From Mozilla Bug 550184:
https://bugzilla.mozilla.org/show_bug.cgi?id=550184
567 int vorbis_analysis_headerout(vorbis_dsp_state *v,
568 vorbis_comment *vc,
569 ogg_packet *op,
570 ogg_packet *op_comm,
571 ogg_packet *op_code){
574 oggpack_buffer opb;
575 private_state *b=v->backend_state;
577 if(!b){
578 ret=OV_EFAULT;
579 goto err_out;
630 err_out:
631 oggpack_writeclear(&opb);