Blender Git Loki

Potential fix for T81963: Random crashes in liboverride code.

From the backtrace it looks like in some cases file save (which triggers
a general override updates) is done before other code has a chance to
re-generate pose data, leading to rna accessing freed memory.

I was never able to reproduce that here, so this is a tentative fix in
master, if it proves to be working for the studio it will be
cherry-picked into 2.91 release branch later.