Afegit un lock per evitar que es puga incrementar el poder de la fase

Es necesita almenys un jugador viu per a poder incrementar el poder de la fase

source/player.cpp

@@ -10,6 +10,7 @@
 #include "texture.h"		 // Para Texture
 #include "resource.h"
 #include "jail_audio.h"
+#include "stage.h"
 
 // Constructor
 Player::Player(int id, float x, int y, bool demo, SDL_Rect &play_area, std::vector<std::shared_ptr<Texture>> texture, const std::vector<std::vector<std::string>> &animations)
@@ -503,6 +504,7 @@ void Player::setPlayingState(PlayerState state)
 		init();
 		playing_state_ = PlayerState::PLAYING;
 		setScoreboardMode(ScoreboardMode::SCORE);
+		Stage::power_can_be_added = true;
 		break;
 	}
 	case PlayerState::CONTINUE: