gui: Call setWalletActionsEnabled(true) only for the first wallet
gui: Call setWalletActionsEnabled(true) only for the first wallet

Summary:
> On master there is a bug:
>  - open an encrypted wallet; please note that the "Encrypt Wallet..." menu item is disabled that is expected
>  - then open any other wallet; note that the "Encrypt Wallet..." menu item gets enabled that is wrong
> This PR fixes this bug.

This is a backport of [[https://github.com/bitcoin-core/gui/pull/43 | core-gui#43]]

Test Plan:
`ninja all check-all`

Failed to reproduce the bug after this change.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10604

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