Improve currency panel

currency_label.gd

@@ -37,6 +37,7 @@ func _on_currency_changed(changed_currency_id: StringName, amount: BigNumber) ->
 	if changed_currency_id != _currency_id:
 		return
 	_currency_label.text = amount.to_string_suffix(2)
+	visible = currency.always_visible or not amount.is_equal_to(BigNumber.from_float(0.0))
 
 func _on_debug_income_button_pressed() -> void:
 	if currency == null: