Blender Git Loki

Fix T86853: Critical bug in write code of CacheFile ID.

CacheFile writing code would not write generic ID data (call for it has
been missing since the initial commit, rB61050f75b13e).

While potentially affecting other areas (mostly CustomProperties/IDProperties),
this was a critical failure for liboverrides. Also added some workaround
code to allow opening broken files (though the override of the CacheFile
data-block will be lost).