Column flicker while sorting a column, when there is lazy loading + hideEmptyGroupColumns

[roblotter]

Codesandbox demo

https://codesandbox.io/s/naughty-cartwright-r1s874

To Reproduce

Steps to reproduce the behavior (in the codesandbox above):

1. Expand a group
2. Sort the age column

Since hideEmptyGroupColumns is true by default, when reloading the datasource, the secondary group column (for the city field) is hidden while loading is in progress and then re-appears when loading is done. This causes an ugly flicker of columns.