RFR: 8280601: ClhsdbThreadContext.java test is triggering codecache related assert in PointerFinder.find()

[Chris Plummer]

It's possible for an address to be in the codecache but not in any CodeBlob. Don't assert in this case.

Note I couldn't reproduce this failure. Not sure why since it seemed to reproduce pretty readily in our CI tier7, and I ran with the same options.

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Commit messages:
 - Don't assert if there is not CodeBlob for codecache address.

Changes: https://git.openjdk.java.net/jdk/pull/7217/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7217&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280601
  Stats: 18 lines in 2 files changed: 8 ins; 2 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7217.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7217/head:pull/7217

PR: https://git.openjdk.java.net/jdk/pull/7217