Merge bitcoin-core#138: unlock encrypted wallet "OK" button bugfix

8008ef7 qt: unlock wallet "OK" button bugfix (Michael Dietz)

Pull request description:

  When trying to send a transaction from an encrypted wallet, the ask
  passphrase dialog would not allow the user to click the "OK" button
  and proceed. Therefore it was impossible to send a transaction
  through the gui. It was not enabling the "OK" button after the
  passphrase was entered by the user, because it was using the same
  form validation logic as the "Change passphrase" flow.

  I reported this in a comment in bitcoin-core#136. But then I realized this seems to be a flat out bug.

ACKs for top commit:
  MarcoFalke:
    review ACK 8008ef7
  hebasto:
    ACK 8008ef7, I have reviewed the code and it looks OK, I agree it can be merged.

Tree-SHA512: cc09b34c7f3aea09729e1c7ccccff05dc11fec56fee2ad369f2d862979572b1edd8b7e738ffe6e91d35d071b819b0c3e0f5d48bf5e27427a80af4a28893f8aaf

Author: MarcoFalke

src/qt/askpassphrasedialog.cpp

@@ -199,6 +199,8 @@ void AskPassphraseDialog::textChanged()
         acceptable = !ui->passEdit2->text().isEmpty() && !ui->passEdit3->text().isEmpty();
         break;
     case Unlock: // Old passphrase x1
+        acceptable = !ui->passEdit1->text().isEmpty();
+        break;
     case ChangePass: // Old passphrase x1, new passphrase x2
         acceptable = !ui->passEdit1->text().isEmpty() && !ui->passEdit2->text().isEmpty() && !ui->passEdit3->text().isEmpty();
         break;