[QA] Public link on a file with Download/View/Edit ignores password enforcement

[jnweiger]

Seen with 10.12.0 (and also 10.11.0, not a regression)

• Visit the admin UI -> sharing, and check all four available password enforcements.
  

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• Create a file public.txt and add a public share with read only permissions.
• Try to leave the password field empty. An error occurs. OK
  

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• Create a file public.txt and add a public share with download edit permissions.
• Leave the password field empty. The share is created. BAD.
• Access the share through the public link, the file can be downloaded. BAD.
  

(Public links on folders work fine. Each of the four link types has its own enforce setting.)