QDrag pixmap is ignored on Windows if no action is available

On Windows, the drag pixmap isn't displayed if the drop effect is none. This is because OleDropSource::createCursors() creates move, copy, and link cursors using the drag pixmap, if set. When QOleDropSource::GiveFeedback() is called, it checks if the drop effect is found in the drag managers list of cursors, and if so uses manager's cursor; otherwise it returns DRAGDROP_S_USEDEFAULTCURSORS and Windows uses the default cursor. Thus, if the effect is DROPEFFECT_NONE, the drag pixmap is ignored. We should include a "no effect" cursors so that the pixmap is always displayed.