Describe the bug

When required is used in b-form-file and a file is dragged, it still shows select a file alert on submit.

It works fine with selecting file from the popup file system.

Steps to reproduce the bug

1. Go to https://codesandbox.io/s/form-required-drag-0uccq
2. Drag a file in the Choose file form.
3. Submit form, it shows alert.
4. Now click on Choose a file and select a file from the selector.
5. Submit form, it works.

Expected behavior

1. Go to https://codesandbox.io/s/form-required-drag-0uccq
2. Drag a file in the Choose file form OR click on Choose a file and select a file from the selector.
3. Submit form. It should work for both methods.