StudioWelcome: silent splashscreen if there is a dialog open

Task-number: QDS-12713
Change-Id: I206f132f526928fb02ea8d2f117c0ba19c08156e
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Qt CI Patch Build Bot <ci_patchbuild_bot@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
(cherry picked from commit cf614eca91)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/studiowelcome/studiowelcomeplugin.cpp

@@ -587,6 +587,9 @@ static bool forceDownLoad()
 
 static bool showSplashScreen()
 {
+    // some error dialog is maybe open, be silent to avoid focus problems (macOS had some)
+    if (Core::ICore::mainWindow() != Core::ICore::dialogParent())
+        return false;
     const Key lastQDSVersionEntry = "QML/Designer/lastQDSVersion";
 
     QtcSettings *settings = Core::ICore::settings();