The rotation of the gradient instead of the shape needs to be
flipped because OOXML flips shapes before rotating them.

Change-Id: I332412078ae0f8d555bd462964c7b20037147e02
Reviewed-on: https://gerrit.libreoffice.org/40136Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>
Tested-by: Tamás Zolnai <tamas.zolnai@collabora.com>