Scattergl tonext case

[dy]

Followed by #2280 - this test case should work with scattergl:

var trace0 = {y: [1, 3, 5, 7], type: 'scattergl'};
var trace1 = {y: [1, 2, 3, 4], type: 'scattergl', line: {width: 0}, mode: 'lines'};
var trace2 = {y: [3, 4, 5, 6], type: 'scattergl', fill: 'tonexty', mode: 'none'};

Plotly.newPlot(gd, [trace0, trace1, trace2], {}, {scrollZoom: true})
.then(function() {
    return Plotly.restyle(gd, {y: [[null, null, null, null]]}, [1]);
})
.then(function() {
    return Plotly.restyle(gd, {y: [[1, 2, 3, 4]]}, [1]);
})
.then(function() {
    return Plotly.restyle(gd, {y: [[null, null, null, null]]}, [2]);
})
.then(function() {
    return Plotly.restyle(gd, {y: [[1, 2, 3, 4]]}, [2]);
})
.then(function() {
    return Plotly.restyle(gd, {y: [[null, null, null, null], [null, null, null, null]]}, [1, 2]);
})
.catch(fail)
.then(done);

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson