Merge branch 'ds/midx-write-fixes' into maint-2.51

Fixes multiple crashes around midx write-out codepaths. * ds/midx-write-fixes: midx-write: simplify error cases midx-write: reenable signed comparison errors midx-write: use uint32_t for preferred_pack_idx midx-write: use cleanup when incremental midx fails midx-write: put failing response value back midx-write: only load initialized packs