Fix portal urls cache on X11

When I was reading QPA code at first, I was thinking that windows and
cocoa QPAs have a QMimeData for all the run time, while xcb and wayland
create them on every owner change. It seems I've misread the xcb code
as the portal cache bugs on it now.

This changes the cache to use the last transfer ID that should make it
unaware of the implementation detail while still allowing the consumer
to get portal urls until another file is copied.

BUG: 460314

src/lib/io/kurlmimedata.cpp

@@ -119,13 +119,14 @@ static QString portalFormat()
 static QList<QUrl> extractPortalUriList(const QMimeData *mimeData)
 {
     Q_ASSERT(QCoreApplication::instance()->thread() == QThread::currentThread());
-    static QHash<const QMimeData*, QList<QUrl>> cache;
-    if (const auto uris = cache.constFind(mimeData); uris != cache.constEnd()) {
-        qCDebug(KCOREADDONS_DEBUG) << "Urls from portal cache" << *uris;
-        return *uris;
-    }
+    static std::pair<QByteArray, QList<QUrl>> cache;
     const auto transferId = mimeData->data(portalFormat());
     qCDebug(KCOREADDONS_DEBUG) << "Picking up portal urls from transfer" << transferId;
+    if (std::get<QByteArray>(cache) == transferId) {
+        const auto uris = std::get<QList<QUrl>>(cache);
+        qCDebug(KCOREADDONS_DEBUG) << "Urls from portal cache" << uris;
+        return uris;
+    }
     auto iface =
         new OrgFreedesktopPortalFileTransferInterface(portalServiceName(), QStringLiteral("/org/freedesktop/portal/documents"), QDBusConnection::sessionBus());
     const QStringList list = iface->RetrieveFiles(QString::fromUtf8(transferId), {});
@@ -135,10 +136,7 @@ static QList<QUrl> extractPortalUriList(const QMimeData *mimeData)
         uris.append(QUrl::fromLocalFile(path));
     }
     qCDebug(KCOREADDONS_DEBUG) << "Urls from portal" << uris;
-    cache.insert(mimeData, uris);
-    QObject::connect(mimeData, &QObject::destroyed, [mimeData] {
-        cache.remove(mimeData);
-    });
+    cache = std::make_pair(transferId, uris);
     return uris;
 }
 #endif