Adding images leads to unreadable file (revisit)

Created originally on Bitbucket by jabbors (Johan Abbors)

This is follow-up on issue #500 (closed).

With openpyxl version 2.3.0 I get unreadable files when I add an image to a workbook. It opens fine with LibreOffice but not with Excel for Mac v15.15.

If I choose the repair the file, the image is there.

Attachments: Screen_Shot_2015-10-30_at_14.10.18