SCI32: Always initialize RobotDecoder::_syncFrame

This flag previously was only being initialized in Robot files
with audio. This means the flag was incorrectly carried to
Robots without audio, and if the first Robot played by the game
had no audio, it would be a garbage read. (This latter thing
happens at the beginning of Lighthouse.)

engines/sci/video/robot_decoder.cpp

@@ -397,8 +397,6 @@ void RobotDecoder::initPlayback() {
 }
 
 void RobotDecoder::initAudio() {
-	_syncFrame = true;
-
 	_audioRecordInterval = RobotAudioStream::kRobotSampleRate / _frameRate;
 
 	_expectedAudioBlockSize = _audioBlockSize - kAudioBlockHeaderSize;
@@ -539,6 +537,7 @@ void RobotDecoder::open(const GuiResourceId robotId, const reg_t plane, const in
 
 	initPlayback();
 
+	_syncFrame = true;
 	_audioBlockSize = _stream->readUint16();
 	_primerZeroCompressFlag = _stream->readSint16();
 	_stream->seek(2, SEEK_CUR); // unused