202210 fix for 37409 checking if property exists before reading it

Created by: ernestob

Description

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

Motivation & Context

Error is thrown when disposing of a modal that is hidden.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed