Fix intermittent geometry entity crash

[hpinkos]

Fixes #3061

The crash was happening because setting show triggered a subscription that added the updater to an showsUpdated associative array and setting polygon.material removed the polygon from the batch but not from showsUpdated. So when Batch.updateShows is called it iterates through showsUpdated and was crashing because the instance no longer exists for the polygon that was removed.

[cesium-concierge]

@hpinkos, thanks for the pull request! Maintainers, we have a signed CLA from @hpinkos, so you can review this at any time.

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[hpinkos]

@bflood-agi @nmschulte This should fix the crashes you reported in #3061
This ended up being a pretty easy fix, sorry we weren't able to look into it sooner! Thanks for giving us information for how to reproduce it

[bflood-agi]

Awesome! Thanks @hpinkos!

[mramato]

Unfortunately, I can still reproduce the problem in this branch.

[mramato]

TypeError: Cannot read property 'id' of undefined
    at Batch.updateShows (https://cesiumjs.org/Cesium/Source/DataSources/StaticGeometryColorBatch.js:265:59)
    at Batch.update (https://cesiumjs.org/Cesium/Source/DataSources/StaticGeometryColorBatch.js:249:18)
    at updateItems (https://cesiumjs.org/Cesium/Source/DataSources/StaticGeometryColorBatch.js:427:34)
    at StaticGeometryColorBatch.update (https://cesiumjs.org/Cesium/Source/DataSources/StaticGeometryColorBatch.js:434:25)
    at GeometryVisualizer.update (https://cesiumjs.org/Cesium/Source/DataSources/GeometryVisualizer.js:253:36)
    at DataSourceDisplay.update (https://cesiumjs.org/Cesium/Source/DataSources/DataSourceDisplay.js:272:37)
    at Viewer._onTick (https://cesiumjs.org/Cesium/Source/Widgets/Viewer/Viewer.js:1569:49)
    at Event.raiseEvent (https://cesiumjs.org/Cesium/Source/Core/Event.js:146:30)
    at Clock.tick (https://cesiumjs.org/Cesium/Source/Core/Clock.js:307:21)
    at CesiumWidget.render (https://cesiumjs.org/Cesium/Source/Widgets/CesiumWidget/CesiumWidget.js:693:43)

[hpinkos]

Dangit, really? I ran the thing forever and it didn't crash.

Do you think I can just add a if (!defined(instance)) { return } in updateShows?

[mramato]

Wait, hold on. I think I screwed up.

[mramato]

Sorry for the scare, I was actually running in the wrong tab and using cesiumjs.org instead of my local build 😄

[mramato]

Yep, this is definitely fixed. I'll merge when green.

[hpinkos]

🎉