This prevented calculation of the pressure data when dragging
planner handles. However, this lead to weird artifacts.
As an alternative, if this turns out to be too slow, we might
disable the plotting of the pressure curves instead.
That said, even on my super-slow fanless laptop, this performs
reasonably.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>