Fix compilation with --disable-muxers.

patch by Gianluigi Tiesi, mplayer==at==netfarm==dot==it

Originally committed as revision 5632 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/wav.c

@@ -201,12 +201,12 @@ int wav_codec_get_id(unsigned int tag, int bps)
     return id;
 }
 
-#ifdef CONFIG_MUXERS
 typedef struct {
     offset_t data;
     offset_t data_end;
 } WAVContext;
 
+#ifdef CONFIG_MUXERS
 static int wav_write_header(AVFormatContext *s)
 {
     WAVContext *wav = s->priv_data;