Each of the Column and Line Chart creates it's own x and y Axes.
So now the LineChart Exporter Method uses the same Axes as the BarChart.

Thanks for the help:
- Balazs Varga
- Adam Kovacs

Change-Id: Ie763cf831c2ce63ef204d1fdcbff634e7ca8fad5
Reviewed-on: https://gerrit.libreoffice.org/64146
Tested-by: Jenkins
Reviewed-by: László Németh <nemeth@numbertext.org>
Reviewed-on: https://gerrit.libreoffice.org/65449