decoder_thread: change the fallback decoder name to "mad"

When there is no Content-Type response header, try the "mad" decoder
plugin.  It uesd to be named "mp3", and we forgot to change the
fallback name in decoder_thread.c.

NEWS

@@ -1,6 +1,7 @@
 ver 0.15.5 (2009/??/??)
 * input:
   - curl: don't abort if a packet has only metadata
+* decoder_thread: change the fallback decoder name to "mad"
 
 
 ver 0.15.4 (2009/10/03)

src/decoder_thread.c

@@ -169,7 +169,7 @@ static void decoder_run_song(const struct song *song, const char *uri)
 		if (plugin == NULL) {
 			/* we already know our mp3Plugin supports streams, no
 			 * need to check for stream{Types,DecodeFunc} */
-			if ((plugin = decoder_plugin_from_name("mp3"))) {
+			if ((plugin = decoder_plugin_from_name("mad"))) {
 				ret = decoder_stream_decode(plugin, &decoder,
 							    &input_stream);
 			}