RFR: 8358230: Incorrect location for the assert for blob != nullptr in CodeBlob::create

[Ashutosh Mehra]

A trivial fix to moves the assert for `blob != nullptr` before any usage of the the `blob`

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Commit messages:
 - 8358230: Incorrect location for the assert for blob != nullptr in CodeBlob::create

Changes: https://git.openjdk.org/jdk/pull/25566/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25566&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358230
  Stats: 3 lines in 1 file changed: 2 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25566.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25566/head:pull/25566

PR: https://git.openjdk.org/jdk/pull/25566