More single-value overlaid histogram fixes

[etpinard]

fixes #3881

where (edge) cases:

• https://codepen.io/etpinard/pen/GaMqYx
• https://codepen.io/etpinard/pen/zQQGbB
• https://codepen.io/etpinard/pen/xNNGBg

were throwing exceptions and failed to render. They now render as:

• https://codepen.io/etpinard/pen/QRRyOq
• https://codepen.io/etpinard/pen/arrdVX
• https://codepen.io/etpinard/pen/qGGbVG

cc @plotly/plotly_js

[archmoj]

Nicely done.
@etpinard Thanks for the fix and codepen demos.
💃