RFR: 8361955: [GCC static analyzer] libjdwp/threadControl.c threadControl_setPendingInterrupt error: dereference of NULL 'node'

[Chris Plummer]

Fix gcc static analyzer warning. It was introduced by [JDK-8324868](https://bugs.openjdk.org/browse/JDK-8324868) early last year. For the most part the fix is to revert the relevant [JDK-8324868](https://bugs.openjdk.org/browse/JDK-8324868) changes, except for leaving in the replacement of calling findThread() with instead calling findRunningThread().

Ran all svc tier2 and tier5 tests.

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Commit messages:
 - fix gcc static analyzer warning

Changes: https://git.openjdk.org/jdk/pull/27378/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27378&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361955
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/27378.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27378/head:pull/27378

PR: https://git.openjdk.org/jdk/pull/27378