The share link field is wrongly active when the "Require a password" checkbox is selected

[Softvision-CristinaBadescu]

[Affected versions]:

• Firefox 57.0.1 and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a file uploaded to https://send.stage.mozaws.net/.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites and navigate to the Share file page.
2. Select the "Require a password" checkbox.
3. Observe the share link field.

[Expected result]:

• The share link field is inactive: the "Copy to clipboard" button is inactionable and has a lighter blue color.

[Actual result]:

• The share link field and "Copy to clipboard" button remain unchanged.

[Notes]:

• This issue is also reproducible on https://send.firefox.com/ and https://send.dev.mozaws.net.
• Here is a screen recording of the issue:
  

[dannycoates]

Since the link doesn't change by adding a password we decided it's ok to keep it enabled. It's working as we now intend it to.