Fix wma2 audio decoder

Patch by Reimar Doeffinger

Originally committed as revision 4779 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/wmadec.c

@@ -284,7 +284,7 @@ static int wma_decode_init(AVCodecContext * avctx)
     }
 
     bps = (float)s->bit_rate / (float)(s->nb_channels * s->sample_rate);
-    s->byte_offset_bits = av_log2((int)(bps * s->frame_len / 8.0)) + 2;
+    s->byte_offset_bits = av_log2((int)(bps * s->frame_len / 8.0 + 0.5)) + 2;
 
     /* compute high frequency value and choose if noise coding should
        be activated */