decoder/Bridge: check for STOP before InputStream::IsReady()

If the DecoderThread gets woken up by a STOP command, this should be
detected as early as possible.

src/decoder/Bridge.cxx

@@ -368,15 +368,15 @@ DecoderBridge::OpenUri(const char *uri)
 
 	const std::lock_guard<Mutex> lock(mutex);
 	while (true) {
+		if (dc.command == DecoderCommand::STOP)
+			throw StopDecoder();
+
 		is->Update();
 		if (is->IsReady()) {
 			is->Check();
 			return is;
 		}
 
-		if (dc.command == DecoderCommand::STOP)
-			throw StopDecoder();
-
 		cond.wait(mutex);
 	}
 }