Purging and removing element while hovering causes "undefined is not an object"

So, I'm unsure if this issue is with the react library or this one. But the responsible code resides in this repository so I'll try my luck here.

If you unmount a plot rendered in react while hovering your mouse over it, maindrag.onmouseout gets triggered before all event handlers are completely unregistered.

This causes the error undefined is not an object (evaluating 'gd._fullLayout._hoversubplot = null') at plotly.js:148662==graph_interact.js:79. I looked into it with a breakpoint and the issue seems to be that _fullLayout doesn't exist anymore on gd.

A simple fix (assuming this is an issue with plotly.js and not react-plotly.js) could be to just add || !dg._fullLayout to graph_interact.js:74. If it isn't an issue with plotly itself, it may still be a good idea to wrap the event handlers with try/catch and log a warning about not unmounting correctly instead of a flat out error.

Start in src/plots/cartesian/graph_interact.js around lines 74-79 and reproduce the failure by unmounting a React-rendered plot while hovering. Verify that the hover cleanup no longer throws when gd._fullLayout is absent, while preserving the normal mouseout behavior.