mempool.dat now contains unbroadcast transactions, that did not exist in
mempool.dat files created in previous version.
This commit prevent an uneccessary error message to be logged when users
update from v0.22.11 or lower.
The try..catch can be removed after everyone has upgraded to > v0.22.11.
This is a backport of Core PR18807 [4/9]
https://github.com/bitcoin/bitcoin/pull/18807/commits/9c8a55d9cb0ec73f10b196e79b637aa601c0a6b7