message: qt, refactor: Replace `if` check with `assert`
  There are no ways BitcoinGUI::updateWalletStatus being called without
  an instance of the WalletFrame class.
diff: @@ -1458,9 +1458,8 @@ void BitcoinGUI::setEncryptionStatus(int status)
  void BitcoinGUI::updateWalletStatus()
  {
  - if (!walletFrame) {
  - return;
  - }
  + assert(walletFrame);
  +
  WalletView * const walletView = walletFrame->currentWalletView();
  if (!walletView) {
  return;
  