Fix transactions disable problem

[beati]

• In bitcoin-qt, there is under Settings the "Mask values" option
• When a wallet is open and the "Mask values" checkbox is checked, the "Transactions" tab is disabled
• When no wallet was open and the "Mask values" checkbox was checked and a wallet was opened, the "Transactions" tab was enabled
• This fix changes this, so that there is always the same behavior
• The "Transactions" tab is now always disabled when the "Mask values" checkbox is checked
• This fix is manually tested on the fork

[DrahtBot]

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Reviews

See the guideline for information on the review process.
A summary of reviews will appear here.

[hebasto]

Does this PR solve the same issue as #815?

[beati]

Does this PR solve the same issue as #815?

Yes, it looks like.
But this PR has a different solution.