[crac] RFR: 8328344: [CRaC] Avoid error when running with -XX:+PerfDisableSharedMem

[Volker Simonis]

CRaC tries to unconditionally restore the hsperf file, even if the checkpointed JVM process was started with `-XX:+PerfDisableSharedMem`.

The fix is trivial: check for the existence of the hsperf file in `PerfMemoryLinux::restore()` just as we already do it in `PerfMemoryLinux::checkpoint()`.

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Commit messages:
 - 8328344: [CRaC] Avoid error when running with -XX:+PerfDisableSharedMem

Changes: https://git.openjdk.org/crac/pull/153/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=153&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328344
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/153.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/153/head:pull/153

PR: https://git.openjdk.org/crac/pull/153