MythMusic: fix playback of ogg radio streams

Peek the probe data from the stream buffer rather than read the data otherwise
ffmpeg fails to open the stream because the magic it is looking for has already
been read from the stream.

Also increase the probe buffer to 16K this seems to be required for some ogg
streams to be probed properly.

mythplugins/mythmusic/mythmusic/avfdecoder.cpp

@@ -48,7 +48,7 @@ extern "C" {
 }
 
 // size of the buffer used for streaming
-#define BUFFER_SIZE 8192
+#define BUFFER_SIZE 16384
 
 // streaming callbacks
 static int ReadFunc(void *opaque, uint8_t *buf, int buf_size)
@@ -264,7 +264,7 @@ bool avfDecoder::initialize()
         probe_data.filename = filename.toLocal8Bit().constData();
         probe_data.buf_size = min(BUFFER_SIZE, (int) input()->bytesAvailable());
         probe_data.buf = m_buffer;
-        input()->read((char*)probe_data.buf, probe_data.buf_size);
+        input()->peek((char*)probe_data.buf, probe_data.buf_size);
         m_inputFormat = av_probe_input_format(&probe_data, 1);
 
         if (!m_inputFormat)