Merge bitcoin-core#774: Fix crash on selecting "Mask values" in transaction view

e26e665 gui: fix crash on selecting "Mask values" in transaction view (Sebastian Falbesoner)

Pull request description:

  This PR fixes a crash bug that can be caused with the following steps:
  - change to the "Transactions" view
  - right-click on an arbitrary transaction -> "Show transaction details"
  - close the transaction detail window again
  - select menu item "Settings" -> "Mask values"

  The problem is that the list of opened dialogs, tracked in the member variable `m_opened_dialogs` (introduced in bitcoin-core#708, commit 4492de1), is only ever appended with newly opened transaction detail dialog pointers, but never removed. This leads to dangling pointers in the list, and if the "Mask values" menu item is selected, a crash is caused in the course of trying to close the opened transaction detail dialogs (see `closeOpenedDialogs()` method). Fix this by removing a pointer of the list if the corresponding widget is destroyed.

ACKs for top commit:
  achow101:
    ACK e26e665
  pablomartin4btc:
    tACK e26e665
  furszy:
    utACK e26e665
  hebasto:
    ACK e26e665, tested on Ubuntu 22.04.

Tree-SHA512: 37885c22abae0ab065b4878bae46fd362f41b09609d081fd59e26bb05474f427b98771ee73f5480526afaef04e016c5ba62c956e0e85a57b6a0f44a905b68a83

Author: hebasto

src/qt/transactionview.cpp

@@ -531,6 +531,9 @@ void TransactionView::showDetails()
         TransactionDescDialog *dlg = new TransactionDescDialog(selection.at(0));
         dlg->setAttribute(Qt::WA_DeleteOnClose);
         m_opened_dialogs.append(dlg);
+        connect(dlg, &QObject::destroyed, [this, dlg] {
+            m_opened_dialogs.removeOne(dlg);
+        });
         dlg->show();
     }
 }