Allow the creation of a pie chart from a view with one row

Problem/Motivation

Sometimes with aggregation we can end up with only one row representing 100percent of what we want to display.

Steps to reproduce

For example we can have a field (A) using an average aggregation and the result is 57.3 for example. We can then create a custom text or use the view simple math field (B) module to display the difference. B = 100 - A = 42.7

Proposed resolution

Allow user to select both column A and B as data provider then adjust the code in the chart style plugin to check if only one row is supposed to be rendered then loops through the columns make them as data row.

Remaining tasks

Submit a patch or merge request.

User interface changes

N/A

API changes

N/A

Data model changes

N/A