Verify that block requests have a hash and that it's correct. This helps
prevent certain races and ensure that only expected data is ever
returned in response to a request.
(In Syncthing prior to 1.28.1 the block hash was omitted for encrypted
requests from trusted devices. This breaks compatibility with that
specific config on those versions.)
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Signed-off-by: Jakob Borg <jakob@kastelo.net>
f6428af4c8