Merge branch 'tb/midx-with-changing-preferred-pack-fix'

Multi-pack index got corrupted when preferred pack changed from one pack to another in a certain way, which has been corrected. * tb/midx-with-changing-preferred-pack-fix: midx.c: avoid adding preferred objects twice midx.c: include preferred pack correctly with existing MIDX midx.c: extract `midx_fanout_add_pack_fanout()` midx.c: extract `midx_fanout_add_midx_fanout()` midx.c: extract `struct midx_fanout` t/lib-bitmap.sh: avoid silencing stderr t5326: demonstrate potential bitmap corruption