[qt] Simplifies boolean expression model && model->haveWatchOnly()

The boolean expression model && model->haveWatchOnly() can be simplified to model->haveWatchOnly(), because if (!model || !model->getOptionsModel()) { return; } guards against a potential dereferenced null pointer.

src/qt/transactionview.cpp

@@ -365,7 +365,7 @@ void TransactionView::exportClicked()
     // name, column, role
     writer.setModel(transactionProxyModel);
     writer.addColumn(tr("Confirmed"), 0, TransactionTableModel::ConfirmedRole);
-    if (model && model->haveWatchOnly())
+    if (model->haveWatchOnly())
         writer.addColumn(tr("Watch-only"), TransactionTableModel::Watchonly);
     writer.addColumn(tr("Date"), 0, TransactionTableModel::DateRole);
     writer.addColumn(tr("Type"), TransactionTableModel::Type, Qt::EditRole);