(more) Problems with single-value overlay histograms

[etpinard]

see https://codepen.io/etpinard/pen/GaMqYx?editors=1010 and more examples in #3845:

• Introducing histogram* bingroup attributes #3845 (comment) - https://codepen.io/etpinard/pen/zQQGbB
• https://github.com/plotly/plotly.js/pull/3845/files#r285291339 - https://codepen.io/etpinard/pen/xNNGBg
• https://github.com/plotly/plotly.js/pull/3845/files#r285291581 - https://codepen.io/etpinard/pen/OYYVGB

Related:

• Histogram edge cases #2028
• Fix yet another histogram edge case #2413