BaseXYPlot creates invalid screen points

[cfarrow]

It is possible to get invalid screen points from a BaseXYPlot.map_screen.

Starting here:
If data_array is 1-dimensional and one of the points is out of bounds, then the LinearMapper being used to map the screen point (here) will return an array. Meanwhile, for the in-bounds point a scalar will be returned (here). Then the BaseXYPlot packs the array and scalar into a single object array which is not the right thing to do.

I think the right solution is to have the BaseXYPlot handle this corner case, but the LinearMapper might be to blame since in both places the proper behavior is not documented.