Regression from commit cf5fa358a6 (PPTX
export: fix missing audio anim node for slide narrations, 2021-01-25),
the problem was that the audio source can be any kind of shape, not only
a media shape.
Fix the problem by explicitly checking of the shape has a media URL.
Change-Id: I2bdde0f9ed3576f307aabff5e39d441f295c203f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113715
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
9ac1d3ac65