tdf#146066 chart: fix automatic axis scaling at dates

tdf#146066 chart: fix automatic axis scaling at dates

Automatic scaling of the Y axis was incorrect
when the X axis was a date axis and the last
Y value was the highest value. To fix this,
increase maximum date value by one month/year.

Regression from commit ed2c880a691a0b179bbc92a8ce4ee49eac004035
(tdf#133005 Chart: fix ODF import of date axis position).

Change-Id: I0989ae8002e55f4ecfaf530ab845badb4409ecf1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128209
Tested-by: László Németh <nemeth@numbertext.org>
Reviewed-by: László Németh <nemeth@numbertext.org>
(cherry picked from commit 81abc0d7657f194804681415a786627ab71475e3)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/129085
Tested-by: Jenkins
Reviewed-by: Tünde Tóth <toth.tunde@nisz.hu>