[worksheet] when doing auto-scaling in the plot, respect the current data…

Authored by Martin Mamsoler <martin.marmsoler@gmail.com> on Aug 10 2019, 1:20 PM.

Description

[worksheet] when doing auto-scaling in the plot, respect the current data ranges.

BUG: 394029
FIXED-IN: 2.7
Differential Revision: https://phabricator.kde.org/D22495