Related: fdo#52226 ensure graphics are swapped in on DrawingML::WriteImage

I imagine it would be best that the Graphics were delivered pre-swapped in by
higher levels in case there are second level caches or more complex caching
systemed wrapped around it, so warn about it in debug mode but give it a
last-ditch shot anyway. i.e. while the .docx problem should be fixed there
is a report of a very similar .xlsx problem

Change-Id: Ie40ee10fe5cba8ff9c321f47b83e33ee2c1425fd