Always have a valid weapon

Fix crash when you're shooting when you die or when you start the game.
Since weapon is nil (waiting for anim to finish before assigning it),
the game crashes trying on Audio.play(weapon.sound_shoot).

objects/player.gd

@@ -51,6 +51,7 @@ func _ready():
 	Input.mouse_mode = Input.MOUSE_MODE_CAPTURED
 	rotation_delta = Vector2.ZERO
 
+	weapon = weapons[weapon_index]  # weapon must never be nil
 	initiate_change_weapon(weapon_index)