Fix `cleanLayout` bug [882]
Fix `cleanLayout` bug [882]

- Bug: if only a `titlefont` but no `title` was set, `cleanTitle`
  would not create the new title structure.

asolagmbh/plotly.js,aburato/plotly.js,plotly/plotly.js,plotly/plotly.js,aburato/plotly.js,etpinard/plotly.js,etpinard/plotly.js,etpinard/plotly.js,plotly/plotly.js,asolagmbh/plotly.js,asolagmbh/plotly.js,plotly/plotly.js