Gallery: No feedback for invalid password

CVSS ---- Low 3.1 [CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N](https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N) Description ----------- The Gallery plugin does not inform a user when password-protecting a file failed in combination with the Password Policy plugin. Because of this, files that the user will rightfully assume to be password-protected are actually publicly accessible. POC --- Prerequisite: Enable Gallery and Password Policy plugins & upload an image View the image in the Gallery: http://192.168.0.103/nextcloud/nextcloud/index.php/apps/gallery/#dummy_192x192.png Now click on "Share" -> "Share link" -> "Password protect" and enter a password that is in violation of the password policy (for example `vjhtdf68`). The password will not actually be applied, as it violates the policy. However, the feedback is exactly the same as when a password is successfully set; there is no error message. A user will now think that the file is password-protected while it is actually publicly accessible. Solution --------- The error should be visibly shown, so that a user is aware that no password is set (the same way as is currently already happening in the main file view when setting a password). ## Impact accidental disclosure of files which should be password protected.