Fix crash on drag-and-drop over panel
The fake drag-and-drop events caused by the panel reuse the real event's mimeData, and were handled asynchronously. By the time the fake event has been dispatched from the event loop, the mimeData may already have been freed. Send the fake events synchronously again.
This effectively reverts commit https://commits.kde.org/plasma-workspace/31b0bf7f199113c73873c451ad0d740072cbbda3