fix replay undo, #2101

ReplayMode::Undo() is in the same threat of the Game::MainLoop(), so the
gMutex.Lock() there is meaningless.

gframe/game.cpp

@@ -735,7 +735,7 @@ void Game::MainLoop() {
 			soundManager.PlayBGM(BGM_DECK);
 			DrawBackImage(imageManager.tBackGround_deck);
 			DrawDeckBd();
-		} else if(!dInfo.isReplaySkiping) {
+		} else {
 			soundManager.PlayBGM(BGM_MENU);
 			DrawBackImage(imageManager.tBackGround_menu);
 		}

gframe/replay_mode.cpp

@@ -106,6 +106,7 @@ int ReplayMode::ReplayThread(void* param) {
 			get_message(pduel, (byte*)engineBuffer);
 			is_continuing = ReplayAnalyze(engineBuffer, len);
 			if(is_restarting) {
+				mainGame->gMutex.Lock();
 				is_restarting = false;
 				int step = current_step - 1;
 				if(step < 0)
@@ -280,7 +281,6 @@ void ReplayMode::Undo() {
 		return;
 	mainGame->dInfo.isReplaySkiping = true;
 	Restart(false);
-	mainGame->gMutex.Lock();
 	Pause(false, false);
 }
 bool ReplayMode::ReplayAnalyze(char* msg, unsigned int len) {