Decoder*: add more assertions

src/DecoderAPI.cxx

@@ -47,6 +47,7 @@ decoder_initialized(Decoder &decoder,
 
 	assert(dc.state == DecoderState::START);
 	assert(dc.pipe != nullptr);
+	assert(dc.pipe->IsEmpty());
 	assert(decoder.stream_tag == nullptr);
 	assert(decoder.decoder_tag == nullptr);
 	assert(!decoder.seeking);
@@ -405,6 +406,9 @@ decoder_data(Decoder &decoder,
 	    length == 0)
 		return cmd;
 
+	assert(!decoder.initial_seek_pending);
+	assert(!decoder.initial_seek_running);
+
 	/* send stream tags */
 
 	if (update_stream_tag(decoder, is)) {

src/DecoderInternal.cxx

@@ -83,6 +83,9 @@ void
 decoder_flush_chunk(Decoder &decoder)
 {
 	DecoderControl &dc = decoder.dc;
+	assert(!decoder.seeking);
+	assert(!decoder.initial_seek_running);
+	assert(!decoder.initial_seek_pending);
 
 	assert(decoder.chunk != nullptr);