lv_chart: Fix division by zero issue when all points are equal (#1962)
lv_chart: Fix division by zero issue when all points are equal (#1962)

* Fix division by zero issue when all points are equal

As the title says, when all the points are equal, it attempts division by zero, and in some cases it can result in funny behavior.
Slightly kludgy fix, but not a significant performance impact.

* Actually fix the division by zero issue both ways

Previous commit was slightly broken and only worked one way

* Fix range setting instead of drawing

* Missing y_tmp
littlevgl/lvgl,littlevgl/lvgl,littlevgl/lvgl,littlevgl/lvgl