UI: Datasets: Turning off all columns for the plot causes it to disappear

[martinjrobins]

Describe the bug

If you select a dataset to visualise, the plot pops up with the "Volt" column selected. Clicking on the "Volt" column turns it off (so no columns are selected). This causes the plot to disappear completely, including the legend, so you can't turn "Volt" or any other column back on

To Reproduce
Steps to reproduce the behavior:

1. Go to Datasets
2. Click on a dataset
3. Scroll down to the plot
4. Click "Volt" column

Expected behavior

The "Volt" column should disappear, leaving the empty plot. The legend should still be visible so you can select another column to display