EMF+: Do not ignore source rectangle of the image to be rendered.

Change-Id: I4f861c7653c89d8f1ca73696e885f33f7bfc3b06
Reviewed-on: https://gerrit.libreoffice.org/6932
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>