Write the correct theme path to the InteropGrabBag, the same path
what is generated and checked in the export code.

Change-Id: I32617c1a11cf3bafb142f7c8839b498aaac49aa0
Reviewed-on: https://gerrit.libreoffice.org/72500
Tested-by: Jenkins
Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>