UI: Fix memory leak with Manage Broadcast dialog

When OBS has been connected to a YouTube account, the Manage Broadcast
dialog becomes available. Opening and closing this dialog leaks about
2-3 MB of memory each time. This happens because the dialog is never
deleted, and a new object is created every time the dialog opens.

If we set Qt::WA_DeleteOnClose on the dialog, then the dialog->exec()
call would call delete this. However, if the dialog->Valid() call
returned false (this should currently be impossible), then exec is never
called, so it would not clean up.

To fix this, make the dialog stack-allocated instead of using new and
delete.

Detected by clang-analyzer.

UI/window-basic-main.cpp

@@ -6668,12 +6668,10 @@ void OBSBasic::SetupBroadcast()
 #if YOUTUBE_ENABLED
 	Auth *const auth = GetAuth();
 	if (IsYouTubeService(auth->service())) {
-		OBSYoutubeActions *dialog;
-		dialog = new OBSYoutubeActions(this, auth, broadcastReady);
-		connect(dialog, &OBSYoutubeActions::ok, this,
+		OBSYoutubeActions dialog(this, auth, broadcastReady);
+		connect(&dialog, &OBSYoutubeActions::ok, this,
 			&OBSBasic::YouTubeActionDialogOk);
-		int result = dialog->Valid() ? dialog->exec()
-					     : QDialog::Rejected;
+		int result = dialog.Valid() ? dialog.exec() : QDialog::Rejected;
 		if (result != QDialog::Accepted) {
 			if (!broadcastReady)
 				ui->broadcastButton->setChecked(false);