Debugger: Use dialogParent instead of mainWindow

Slipped through in 5b364de168

Change-Id: If316f7310b3861630b58ef9f8fb152cc30de8ef1
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/watchhandler.cpp

@@ -2463,7 +2463,7 @@ void WatchModel::clearWatches()
         return;
 
     const QDialogButtonBox::StandardButton ret = CheckableMessageBox::doNotAskAgainQuestion(
-                ICore::mainWindow(), tr("Remove All Expression Evaluators"),
+                ICore::dialogParent(), tr("Remove All Expression Evaluators"),
                 tr("Are you sure you want to remove all expression evaluators?"),
                 ICore::settings(), "RemoveAllWatchers");
     if (ret != QDialogButtonBox::Yes)