Fix for #873

[patorjk]

#873

Quick view: https://codesandbox.io/s/github/patorjk/mui-datatables/tree/sortFail

For test, change customizeFilter example to:

import { FormGroup, FormLabel, TextField } from '@material-ui/core';
import React from 'react';
import ReactDOM from 'react-dom';
import MUIDataTable from '../../src';

class Example extends React.Component {
  render() {
    const data = [
      {
        foo: 1,
        bar: 2
      },
      {
        foo: 3
      }
    ];

    const columns = [
      {
        name: "foo"
      },
      {
        name: "bar"
      }
    ];

    var options = {
      responsive: "scroll"
    };

    return (
      <MUIDataTable title={'ACME Employee list - customizeFilter'} data={data} columns={columns} options={options} />
    );
  }
}

ReactDOM.render(<Example />, document.getElementById('app-root'));

[coveralls]

Coverage increased (+0.07%) to 75.297% when pulling 73d6889 on patorjk:sortFail into d1914e4 on gregnb:master.

[patorjk]

Also, when I updated the sortCompare function, I changed it so it wouldn't have any side effects (previously it was modifying a.data and b.data if they were null). The function is only used in 1 place in the code:

https://github.com/gregnb/mui-datatables/blob/master/src/MUIDataTable.js#L1133

The returned sortedData array only gets used for positional information, so the previous side effect didn't have any affect, so it should be safe to remove.

[gabrielliwerant]

Nice catch! Looks good to go. I also added a test #892 to hopefully prevent regressions here in the future.