Custom hover event for pie chart fail when hoverinfo set to 'none'

[yongjun21]

https://github.com/plotly/plotly.js/blob/master/src/traces/pie/plot.js#L99
https://github.com/plotly/plotly.js/blob/master/src/traces/pie/plot.js#L129

handleMouseOver exit early if hoverinfo set to 'none' skipping Fx.hover which triggers the custom hover event

[etpinard]

related to #851