Make CCryptoKeyStore::Unlock check all keys.

CCryptoKeyStore::Unlock has a loop to attempt decrypting each key which
 only executes once, likely due to a simple mistake when the code was
 originally written.

This patch fixes the behavior by making it check all keys. It also adds
 a fatal assertion in the case some decrypt but some do not, since that
 indicates that the wallet is in some kind of really bad state.

This may make unlocking noticeably slower on wallets with many keys.
Dont run full check every time we decrypt wallet.
Merge pull request #4670

a35b55b Dont run full check every time we decrypt wallet. (Matt Corallo)
1e21c17 Make CCryptoKeyStore::Unlock check all keys. (Gregory Maxwell)