aacenc: Properly pad extradata.

This fixes a valgrind error when encoding to ADTS.

Originally committed as revision 23866 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/aacenc.c

@@ -191,7 +191,7 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
 
     s->samples            = av_malloc(2 * 1024 * avctx->channels * sizeof(s->samples[0]));
     s->cpe                = av_mallocz(sizeof(ChannelElement) * aac_chan_configs[avctx->channels-1][0]);
-    avctx->extradata      = av_malloc(2);
+    avctx->extradata      = av_mallocz(2 + FF_INPUT_BUFFER_PADDING_SIZE);
     avctx->extradata_size = 2;
     put_audio_specific_config(avctx);