qt: Poll ShutdownTimer after init is done

Summary:
Backport of Core PR12377
bitcoin/bitcoin#12377

Test Plan: `ninja check check-functional`

Reviewers: deadalnix, Fabien, #bitcoin_abc, markblundeberg

Reviewed By: #bitcoin_abc, markblundeberg

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2545

src/qt/bitcoin.cpp

@@ -374,7 +374,6 @@ void BitcoinApplication::createWindow(const Config *config,
     pollShutdownTimer = new QTimer(window);
     connect(pollShutdownTimer, SIGNAL(timeout()), window,
             SLOT(detectShutdown()));
-    pollShutdownTimer->start(200);
 }
 
 void BitcoinApplication::createSplashScreen(const NetworkStyle *networkStyle) {
@@ -535,6 +534,8 @@ void BitcoinApplication::initializeResult(bool success) {
             window, SLOT(message(QString, QString, unsigned int)));
     QTimer::singleShot(100, paymentServer, SLOT(uiReady()));
 #endif
+
+    pollShutdownTimer->start(200);
 }
 
 void BitcoinApplication::shutdownResult() {