MAD Decoder: Correctly prepare buffer after free

The current buffer size argument is used to determine if a buffer should
be allocated on the next run. Just in case something reuses the same
decoder instance.

Signed-off-by: Christopher Snowhill <kode54@gmail.com>

Plugins/MAD/MADDecoder.m

@@ -631,6 +631,7 @@
 	if(_outputBuffer) {
 		free(_outputBuffer);
 		_outputBuffer = NULL;
+		_currentOutputFrames = 0;
 	}
 
 	mad_synth_finish(&_synth);