124966: keep picture format information - <GfxLink> instance - also for the reading of preview picture data in order to avoid trouble on save in case that the preview data equals the picture data

	cherry-picked from trunk



git-svn-id: https://svn.apache.org/repos/asf/openoffice/branches/AOO410@1603774 13f79535-47bb-0310-9956-ffa450edef68