Explorer: fix error when clicking outside the modal

[jonty007]

If I first click in the modal window, and then outside of the modal, an error is displayed:

Cannot read properties of null (reading 'remove')
TypeError: Cannot read properties of null (reading 'remove')
    at Modal._destroyBackdropEl (http://localhost:1032/static/js/bundle.js:23043:49)
    at Modal.hide (http://localhost:1032/static/js/bundle.js:23134:12)
    at Modal._handleOutsideClick (http://localhost:1032/static/js/bundle.js:23069:12)
    at HTMLDivElement._clickOutsideEventListener (http://localhost:1032/static/js/bundle.js:23050:15)