After a recent commit, multiple drawings were always written using the
same address because we used the same stack memory in a loop. This
causes the blend file reading to not be able to distinguish between the
structs, meaning the file is corrupt. However, we already had the same
problem in some cases because of the inline buffer in `BlendWriteData`.
To resolve this, make all "temporary" data for writing live as long as
the writing is going on for the ID. This is somewhat inefficient since
it makes memory reuse impossible for this temporary data. In the future
we should use a technique like #127706 to address this.
For testing, I saved and loaded multiple production files with Grease
Pencil objects, with and without the "write with attribute storage"
option enabled. The fix still goes to 4.5 though, because the first
mentioned issue is present there, and the `CustomDataLayer` vector
address reuse is potentially a problem too.
Pull Request: https://projects.blender.org/blender/blender/pulls/140667
e82a051ade