[release/2.8] Fix panic in inmemory driver

[wy65701436]

• backport of Fix panic in inmemory driver #3615
• closes TestFileReaderSeek fails on go1.18 #3614

[thaJeztah]

Hm, right so looks like this fails because it's installing "github.com/vbatts/git-validation" "latest", which installs a version of golang.org/x/sys that's incompatible with go1.16

cd /tmp && go get -u github.com/vbatts/git-validation


....

# golang.org/x/sys/unix
Error: /home/runner/work/distribution/distribution/src/golang.org/x/sys/unix/syscall.go:83:16: undefined: unsafe.Slice
Error: /home/runner/work/distribution/distribution/src/golang.org/x/sys/unix/syscall_linux.go:1018:20: undefined: unsafe.Slice
Error: /home/runner/work/distribution/distribution/src/golang.org/x/sys/unix/syscall_linux.go:2297:9: undefined: unsafe.Slice
Error: /home/runner/work/distribution/distribution/src/golang.org/x/sys/unix/syscall_unix.go:118:7: undefined: unsafe.Slice
Error: /home/runner/work/distribution/distribution/src/golang.org/x/sys/unix/sysvshm_unix.go:33:7: undefined: unsafe.Slice
Error: Process completed with exit code 2.

[thaJeztah]

LGTM

(failure is not related, as described above)

[milosgajdos]

LGTM. This attempts to rip out https://github.com/distribution/distribution/pull/3812/files#r1038982612 from #3812 and we are aware of what the issue is hence approving and merging so we can get #3812 merged in.