[jdk21u-dev] RFR: 8344361: Restore null return for invalid services from legacy providers

[Paul Hohensee]

Backport for parity with Oracle 21.0.8. Clean, low risk: obvious bug, updated and new test pass, Provider tests pass: test/jdk/java/security/Provider and test/jdk/sun/security/pkcs11/Provider.

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Commit messages:
 - Backport e20bd018c4046870d0cf632bb8e5440cb9f5c3c2

Changes: https://git.openjdk.org/jdk21u-dev/pull/1600/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1600&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344361
  Stats: 50 lines in 2 files changed: 50 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1600.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1600/head:pull/1600

PR: https://git.openjdk.org/jdk21u-dev/pull/1600