p2p: Avoid prematurely clearing download state for other peers
Summary:
Avoid letting one peer send us data that clears out the download request (and related timers etc) from another peer. The exception is if a block is definitely stored to disk, in which case we'll clear the download state (just as we do for compact blocks).
Backport of core#27608.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D16879