decoder/API: decoder_open_uri() can throw StopDecoder

src/decoder/DecoderAPI.cxx

@@ -275,7 +275,7 @@ decoder_open_uri(Decoder &decoder, const char *uri)
 			return is;
 
 		if (dc.command == DecoderCommand::STOP)
-			return nullptr;
+			throw StopDecoder();
 
 		cond.wait(mutex);
 	}

src/decoder/DecoderAPI.hxx

@@ -118,8 +118,9 @@ void
 decoder_seek_error(Decoder &decoder);
 
 /**
- * Open a new #InputStream and wait until it's ready.  Can get
- * cancelled by DecoderCommand::STOP (returns nullptr).
+ * Open a new #InputStream and wait until it's ready.
+ *
+ * Throws #StopDecoder if DecoderCommand::STOP was received.
  *
  * Throws std::runtime_error on error.
  */