Merge #773: Check for private keys disabled before attempting unlock

517c7f9 gui: Check for private keys disabled before attempting unlock (Andrew Chow)

Pull request description:

  Before trying to unlock a wallet, first check if it has private keys disabled. If so, there is no need to unlock.

  Note that such wallets are not expected to occur in typical usage. However bugs in previous versions allowed such wallets to be created, and so we need to handle them.

  Fixes #772

  For some additional context, see #631

ACKs for top commit:
  hebasto:
    ACK 517c7f9, I have reviewed the code and it looks OK.
  BrandonOdiwuor:
    ACK 517c7f9

Tree-SHA512: c92aa34344d04667b70b059d2aa0a1da999cb7239cd1413f3009781aa82379f309ff9808d7dc91d385e2c8afe2abda3564568e2091ef833b1536ebfcf80f7c3c

src/qt/walletmodel.cpp

@@ -448,6 +448,13 @@ void WalletModel::unsubscribeFromCoreSignals()
 // WalletModel::UnlockContext implementation
 WalletModel::UnlockContext WalletModel::requestUnlock()
 {
+    // Bugs in earlier versions may have resulted in wallets with private keys disabled to become "encrypted"
+    // (encryption keys are present, but not actually doing anything).
+    // To avoid issues with such wallets, check if the wallet has private keys disabled, and if so, return a context
+    // that indicates the wallet is not encrypted.
+    if (m_wallet->privateKeysDisabled()) {
+        return UnlockContext(this, /*valid=*/true, /*relock=*/false);
+    }
     bool was_locked = getEncryptionStatus() == Locked;
     if(was_locked)
     {