647927a330
For IDProperties, this flag is mostly used only to controll whether IDProperty code should also handle ID refcounting or not (through `LIB_ID_CREATE_NO_USER_REFCOUNT`). Without this fix, IDProp Group Merge could end up trying to modify ID refcount of its data-block properties (via `IDP_FreeProperty`), which can lead to data corruption or even crashes (e.g. when used in readfile code, before lib-linking process). Issue discovered while working on the system IDProperties split project (!135807). Pull Request: https://projects.blender.org/blender/blender/pulls/139230