Fix bug that appeared when indirect objects were added to xref.
Indirect objects appearing in trailers of modified documents were
causing access to incompletely constructed xref entries.
Merge commit '2dd554f55aae4ad378b99c14fe545a6c18b9a465'
Save and restore position before and after seeks to read so that writes don't know the file position moved.
Don't clone an indirect reference in Indirect.Clone().