This prevents zooming out to more than max in the planner. Using a Mac
MagicMouse it happens at times that the finger slides on the mouse while
dragging a waypoint which can result in zooming out further than max.
Fixes#695
Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>