Disposing a modal after hiding it triggers an error.

Created by: ernestob

It is necessary to check if the focus value exists before trying to read it. Without this, disposing of a modal after hiding it triggers the following error.

Uncaught TypeError: Cannot read properties of null (reading 'focus')

https://github.com/twbs/bootstrap/blob/961d5ff9844372a4e294980c667bbe7e0651cdeb/js/src/modal.js#L191

Here is the example: https://codepen.io/ernestobr/pen/zYarvQq