Enhancement: Leave password field in share dialog enabled on errors

The password line edit used to be disabled because the related checkbox was unchecked upon errors
such as failing to satisfy the requirements imposed by the "password policy" server app.

Now, the checkbox will not be unchecked, leaving the line edit enabled and keeping the focus on
it. This allows users to enter a new password and try again without having to enable the checkbox
and clicking into the line edit again.

https://github.com/owncloud/client/issues/9336
https://github.com/owncloud/client/pull/9508
