Fix crash in Viewer
Fix crash in Viewer

Clicking on a DynamicObject without a position property causes an exception.
This is a regression introduced in the Viewer refactor.

likangning93/cesium,omh1280/cesium,AnalyticalGraphicsInc/cesium,oterral/cesium,kiselev-dv/cesium,jason-crow/cesium,omh1280/cesium,omh1280/cesium,aelatgt/cesium,denverpierce/cesium,denverpierce/cesium,CesiumGS/cesium,hodbauer/cesium,hodbauer/cesium,likangning93/cesium,AnimatedRNG/cesium,likangning93/cesium,aelatgt/cesium,denverpierce/cesium,jasonbeverage/cesium,denverpierce/cesium,oterral/cesium,jason-crow/cesium,soceur/cesium,emackey/cesium,AnimatedRNG/cesium,oterral/cesium,kiselev-dv/cesium,CesiumGS/cesium,wallw-bits/cesium,josh-bernstein/cesium,emackey/cesium,ggetz/cesium,aelatgt/cesium,kiselev-dv/cesium,emackey/cesium,CesiumGS/cesium,NaderCHASER/cesium,geoscan/cesium,ggetz/cesium,hodbauer/cesium,soceur/cesium,jason-crow/cesium,josh-bernstein/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium,NaderCHASER/cesium,progsung/cesium,esraerik/cesium,AnimatedRNG/cesium,omh1280/cesium,esraerik/cesium,emackey/cesium,esraerik/cesium,wallw-bits/cesium,kiselev-dv/cesium,aelatgt/cesium,soceur/cesium,wallw-bits/cesium,ggetz/cesium,ggetz/cesium,wallw-bits/cesium,CesiumGS/cesium,kaktus40/cesium,progsung/cesium,jason-crow/cesium,geoscan/cesium,likangning93/cesium,CesiumGS/cesium,AnimatedRNG/cesium,YonatanKra/cesium,NaderCHASER/cesium,jasonbeverage/cesium,esraerik/cesium,kaktus40/cesium,likangning93/cesium,YonatanKra/cesium,YonatanKra/cesium