Merge #16135: gui: Set progressDialog to nullptr

d2ae6be80f6a0156021bf8c9b9d17cd4966ddffc gui: Set progressDialog to nullptr (João Barbosa)

Pull request description:

  If a progress notification `> 0` arrives immediately after notification `= 100` then `progressDialog` is a dangling pointer.

  Potential fix for #16134.

ACKs for commit d2ae6b:
  hebasto:
    utACK d2ae6be80f6a0156021bf8c9b9d17cd4966ddffc
  fanquake:
    tACK d2ae6be80f

Tree-SHA512: 300ddde2f27c494b19a5bd4085400d0f5a1d4980fe8cc3c07bfebb037efc35f777215ff1a095eeb16658407e11f04456137393e88a12fdd767b7aac5f12eab5e

src/qt/bitcoingui.cpp

@@ -1744,6 +1744,7 @@ void BitcoinGUI::showProgress(const QString &title, int nProgress)
         {
             progressDialog->close();
             progressDialog->deleteLater();
+            progressDialog = nullptr;
         }
     }
     else if (progressDialog)

src/qt/walletview.cpp

@@ -400,6 +400,7 @@ void WalletView::showProgress(const QString &title, int nProgress)
         {
             progressDialog->close();
             progressDialog->deleteLater();
+            progressDialog = nullptr;
         }
     }
     else if (progressDialog) {