accounts: properly close account manager and usb wallets

[holiman]

I noticed, when interacting both via geth and clef, that shutting down the process and trying to work with usb hardware wallets again, most often failed. I had to unplug the device and plug it back again for it to work.

It turns out that the account manager did not call Close on the wallets that it was managing.
Further, clef did not even bother to close the account manager.

This PR fixes both problems.

[MariusVanDerWijden]

LGTM, the double checking of w.device looked odd to me, but I convinced myself that it is actually needed since the status might change between the moment we hold the read lock and the write lock

[holiman]

LGTM, the double checking of w.device looked odd to me, but I convinced myself that it is actually needed since the status might change between the moment we hold the read lock and the write lock

I wish I could say that I just "saw" that it was needed, but no, I ran into a nil deref first time around, so yeah it was needed :)