Corruption bug fixed by 6.0.25

[finnschiermer]

This is an issue created after the fix that went in to 6.0.25 without its own PR.

It is created to make it easy to refer to this bug from other issues.

The bug is caused by a reallocation of an array without properly updating the parent array with the relocated ref. This can cause various forms of corruption. Corruption can hit in-memory state (inside a write transaction), but we have confirmed that the realm file itself can also be corrupted.