…pool.dat file with a malformed time field

ee11a41 Avoid signed integer overflow when loading a mempool.dat file with a malformed time field (practicalswift)

Pull request description:

  Avoid signed integer overflow when loading a `mempool.dat` file with a malformed time field.

  Avoid the following signed integer overflow:

  ```
  $ xxd -p -r > mempool.dat-crash-1 <<EOF
  0100000000000000000000000004000000000000000000000000ffffffff
  ffffff7f00000000000000000000000000
  EOF
  $ cp mempool.dat-crash-1 ~/.bitcoin/regtest/mempool.dat
  $ UBSAN_OPTIONS="print_stacktrace=1:halt_on_error=1:report_error_type=1" src/bitcoind -regtest
  validation.cpp:5079:23: runtime error: signed integer overflow: 9223372036854775807 + 1209600 cannot be represented in type 'long'
      #0 0x5618d335197f in LoadMempool(CTxMemPool&) src/validation.cpp:5079:23
      #1 0x5618d3350df3 in CChainState::LoadMempool(ArgsManager const&) src/validation.cpp:4217:9
      #2 0x5618d2b9345f in ThreadImport(ChainstateManager&, std::vector<boost::filesystem::path, std::allocator<boost::filesystem::path> >, ArgsManager const&) src/init.cpp:762:33
      #3 0x5618d2b92162 in AppInitMain(util::Ref const&, NodeContext&, interfaces::BlockAndHeaderTipInfo*)::$_14::operator()() const src/init.cpp:1881:9
  ```

  This PR was broken out from PR bitcoin#20089. Hopefully this PR is trivial to review.

  Fixes a subset of bitcoin#19278.

ACKs for top commit:
  MarcoFalke:
    review ACK ee11a41
  Crypt-iQ:
    crACK ee11a41

Tree-SHA512: 227ab95cd7d22f62f3191693b455eacfa8e36534961bee12c622fc9090957cfb29992eabafa74d806a336e03385aa8f98b7ce734f04b0b400e33aa187d353337

…malformed time field

Summary: This is a backport of [[bitcoin/bitcoin#20372 | core#20372]]

Test Plan:
This causes an error before applying the commit, and it works after the change:
```
$ cmake .. -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DENABLE_SANITIZERS=undefined
$ xxd -p -r > mempool.dat-crash-1 <<EOF
0100000000000000000000000004000000000000000000000000ffffffff
ffffff7f00000000000000000000000000
EOF
$ cp mempool.dat-crash-1 /bitcoinddata/regtest/mempool.dat
$ ninja
$ UBSAN_OPTIONS="print_stacktrace=1:halt_on_error=1:report_error_type=1" src/bitcoind -regtest
```

```
../src/validation.cpp:5853:23: runtime error: signed integer overflow: 9223372036854775807 + 1209600 cannot be represented in type 'long'
    #0 0x55f14103ffcd in LoadMempool(Config const&, CTxMemPool&) /home/pierre/dev/bitcoin-abc/build_ubsan/../src/validation.cpp:5853:23
    #1 0x55f14103fb65 in CChainState::LoadMempool(Config const&, ArgsManager const&) /home/pierre/dev/bitcoin-abc/build_ubsan/../src/validation.cpp:4821:9
...
```

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10725