RFR: 8276227: ciReplay: SIGSEGV if classfile for replay compilation is not present after JDK-8275868

[Christian Hagedorn]

The fix for [JDK-8275868](https://bugs.openjdk.java.net/browse/JDK-8275868) does not handle the case when the classfile for the method to be replay compiled is not present. This will fail to load the klass. Afterwards, we are trying to access the protection domain of the failed to load klass (i.e. a null pointer) which results in a segmentation fault. The fix is straight forward to only set the new protection domain if the klass was loaded successfully. I additionally changed the code such that we are only trying to set the protection domain when reading the first `instanceKlass` entry. This avoids some potential problems with older replay files where we do not have this additional first entry set by JDK-8275868.

Thanks,
Christian

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Commit messages:
 - 8276227: ciReplay: SIGSEGV if classfile for replay compilation is not present after JDK-8275868

Changes: https://git.openjdk.java.net/jdk/pull/6189/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6189&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276227
  Stats: 9 lines in 1 file changed: 8 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6189.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6189/head:pull/6189

PR: https://git.openjdk.java.net/jdk/pull/6189