inserted-object writes corrupt .gnumeric file

Follow-on to #481 (closed)

Here is the recipe for creating a corrupt output file, starting from a new blank spreadsheet, using the insert-object feature. The "#" comments in the typescript tell what I was doing. Let me know if additional detail is desired. corrupted-spreadsheet.logg

Here is the trivial spreadsheet that was inserted: foo.gnumeric

Here is the corrupted spreadsheet that was written: bar.gnumeric

Again, not a high priority. We agree the feature has limited utility.