Does not export images/files that are part of Text block

If a text block contains an image it just generates this xml:
```
<concrete-picture fid="f10c1561-237b-4f83-87bf-4063c677b343" alt="myimage.jpg" />
```
But this file is not part of the zip. I think this is a bug? Image blocks are working with the `{ccm:export:file:...}` thing.