wal: fix crc mismatch crash bug

[tangcong]

fix #11918

[gyuho]

/cc @jpbetz

[codecov-commenter]

Codecov Report

Merging #11924 into master will decrease coverage by 0.26%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master   #11924      +/-   ##
==========================================
- Coverage   66.34%   66.07%   -0.27%     
==========================================
  Files         403      403              
  Lines       37245    37250       +5     
==========================================
- Hits        24709    24614      -95     
- Misses      11017    11113      +96     
- Partials     1519     1523       +4     

Impacted Files	Coverage Δ
wal/wal.go	58.50% <60.00%> (+0.01%)	⬆️
auth/options.go	37.50% <0.00%> (-30.00%)	⬇️
client/client.go	53.26% <0.00%> (-20.27%)	⬇️
auth/simple_token.go	79.83% <0.00%> (-9.25%)	⬇️
clientv3/namespace/watch.go	87.87% <0.00%> (-6.07%)	⬇️
etcdserver/api/v3rpc/lease.go	77.21% <0.00%> (-5.07%)	⬇️
raft/tracker/inflights.go	91.83% <0.00%> (-4.09%)	⬇️
proxy/grpcproxy/watcher.go	89.79% <0.00%> (-4.09%)	⬇️
pkg/testutil/recorder.go	77.77% <0.00%> (-3.71%)	⬇️
clientv3/concurrency/election.go	79.68% <0.00%> (-2.35%)	⬇️
... and 18 more

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[tangcong]

=== RUN   TestValidSnapshotEntriesAfterPurgeWal
{"level":"info","msg":"created a new WAL segment","path":"/var/folders/g4/c6b5qg7x05z52phyxcb6wtlm0000gn/T/waltest889121245/0000000000000001-0000000000000002.wal"}
{"level":"info","msg":"created a new WAL segment","path":"/var/folders/g4/c6b5qg7x05z52phyxcb6wtlm0000gn/T/waltest889121245/0000000000000002-0000000000000004.wal"}
    TestValidSnapshotEntriesAfterPurgeWal: wal_test.go:1105: walpb: crc mismatch
--- FAIL: TestValidSnapshotEntriesAfterPurgeWal (0.08s)
FAIL

@gyuho @jpbetz i added a testcase to reproduce it,it is easy to reproduce it. could we need to release a new 3.4/3.3 version ?

[gyuho]

lgtm, I will backport with new release. Thanks for the fix!

/cc @jpbetz

[jpbetz]

Yikes. This is my fault. Thanks for fixing.

lgtm