images: don't try to clip <image> is clip axes are blank
images: don't try to clip <image> is clip axes are blank

- looks like the browsers ignored clip paths that have
  corresponding no <defs> item, but not all renders can
  support them (e.g. Batik - which lead to eps and pdf export
  failures).

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