e2: if one type of files merged and another no - erigon threat is as `gap` (and skip all recent files)

[AskAlexSharov]

after kill -9 in the middle of the merge:

integration print_stages --datadir=/mnt/erigon/ --chain="$CHAIN" --log.console.verbosity=4
DBUG[05-27|02:59:23.846] [snapshots] see gap                      type=transactions from=34130000
DBUG[05-27|02:59:23.846] [snapshots] see gap                      type=transactions from=34130000
INFO[05-27|02:59:29.714] [snapshots:blocks] Stat                  blocks=34130k indices=34130k alloc=1.6GB sys=1.6GB

ls v1-0341*seg
v1-034100-034110-bodies.seg
v1-034100-034110-headers.seg
v1-034100-034110-transactions.seg
v1-034110-034120-bodies.seg
v1-034110-034120-headers.seg
v1-034110-034120-transactions.seg
v1-034120-034130-bodies.seg
v1-034120-034130-headers.seg
v1-034120-034130-transactions.seg
v1-034130-034131-transactions.seg
v1-034130-034140-bodies.seg
v1-034130-034140-headers.seg
v1-034131-034132-transactions.seg
v1-034132-034133-transactions.seg
v1-034133-034134-transactions.seg
v1-034134-034135-transactions.seg
v1-034135-034136-transactions.seg
v1-034136-034137-transactions.seg
v1-034137-034138-transactions.seg
v1-034138-034139-transactions.seg
v1-034139-034140-transactions.seg
v1-034140-034141-bodies.seg
v1-034140-034141-headers.seg
v1-034140-034141-transactions.seg

[yperbasis]

Fixed in main by PRs #10488 & #10514 and in release/2.60 by PR #10487.