If anybody adds a new modal in the `then()` part of the promise, without this code, all `.modal-backdrop` elements will be deleted, and further dialogs will not be modal; with this, only the current modal's backdrop will be deleted.
If anybody adds a new modal in the `then()` part of the promise, without this code, all `.modal-backdrop` elements will be deleted, and further dialogs will not be modal; with this, only the current modal's backdrop will be deleted.