handleCommand_Breath mustn't update breath is player is dead. A dead player doesn't breath.

Add Player::isDead function to check player is dead

src/player.h

@@ -238,6 +238,9 @@ public:
 			inventory.setModified(x);
 	}
 
+	// Use a function, if isDead can be defined by other conditions
+	bool isDead() { return hp == 0; }
+
 	bool touching_ground;
 	// This oscillates so that the player jumps a bit above the surface
 	bool in_liquid;