RFR: 8337782: Use THROW_NULL instead of THROW_0 in pointer contexts in prims code

[Kim Barrett]

Please review this trivial change that, in places in prims code where a
pointer value is required, replaces uses of THROW_0 and THROW_MSG_0 with
THROW_NULL and THROW_MSG_NULL respectively.

Testing: mach5 tier1

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Commit messages:
 - fix THROW_0 in prims

Changes: https://git.openjdk.org/jdk/pull/20456/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20456&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337782
  Stats: 47 lines in 6 files changed: 0 ins; 0 del; 47 mod
  Patch: https://git.openjdk.org/jdk/pull/20456.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20456/head:pull/20456

PR: https://git.openjdk.org/jdk/pull/20456