qt: Stop the effect of hidden widgets on the size of QStackedWidget

Layouts of the hidden widgets, those are children of QStackedWidget,
could prevent to adjust the size of the parent widget in the
WalletFrame widget.

Github-Pull: bitcoin-core/gui#176
Rebased-From: af58f5b
(cherry picked from commit bdc64c9)

src/qt/walletframe.cpp

@@ -106,9 +106,24 @@ void WalletFrame::setCurrentWallet(WalletModel* wallet_model)
 {
     if (mapWalletViews.count(wallet_model) == 0) return;
 
+    // Stop the effect of hidden widgets on the size hint of the shown one in QStackedWidget.
+    WalletView* view_about_to_hide = currentWalletView();
+    if (view_about_to_hide) {
+        QSizePolicy sp = view_about_to_hide->sizePolicy();
+        sp.setHorizontalPolicy(QSizePolicy::Ignored);
+        view_about_to_hide->setSizePolicy(sp);
+    }
+
     WalletView *walletView = mapWalletViews.value(wallet_model);
-    walletStack->setCurrentWidget(walletView);
     assert(walletView);
+
+    // Set or restore the default QSizePolicy which could be set to QSizePolicy::Ignored previously.
+    QSizePolicy sp = walletView->sizePolicy();
+    sp.setHorizontalPolicy(QSizePolicy::Preferred);
+    walletView->setSizePolicy(sp);
+    walletView->updateGeometry();
+
+    walletStack->setCurrentWidget(walletView);
     walletView->updateEncryptionStatus();
 }