Scatterplot facet should show error on non-numeric column

[elebitzero]

Column->Facet->Scatterplot facet requires the selected column to be numeric and at least one other numeric column.

To Reproduce

1. Create Project. Choose sample file foods.csv
2. Next then Create Project
3. Calcium Column -> Facet -> Scatterplot Facet

Current Results

Scatterplot shows a blank dialog when invoked on a non-numeric column.

Expected Behavior

An error message should be displayed.

Screenshots