The commit end of a subheap may be equal to the beginning of another subheap, in
which case find_subheap() will return that one, and we may effectively skip
backwards in the subheap list.
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There may be a more architecturally palatable way to solve this problem, but
hopefully this is enough to at least demonstrate it.
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https://gitlab.winehq.org/wine/wine/-/merge_requests/425