RFR: 8338331: Fix -Wzero-as-null-pointer-constant warnings from CHECK_0 in jni.cpp

[Kim Barrett]

Please review this change to some macros in jni.cpp.  These macros were using
CHECK_0 when calling functions that can "throw" exceptions.  However, the
return type involved is provided by a macro argument, and is a pointer type
for some uses of the macros.  This triggered -Wzero-as-null-pointer-constant
warnings when enabled.

To remove the warnings, these CHECK_0() uses are changed to CHECK_() with an
argument expression that constructs and value-initializes a temporary of that
return type, e.g. `ResultType{}`.  Value-initialization of a scalar type is
zero-initialization. Zero-initialization of a scalar type initializes it to
the value obtained by convertion a literal 0 to that type.  So a zero of the
appropriate type for arithmetic types.  For pointer types it's initialized to
nullptr, without triggering the warning.

Testing: mach5 tier1

-------------

Commit messages:
 - CHECK_0 in jni.cpp

Changes: https://git.openjdk.org/jdk/pull/20575/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20575&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338331
  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/20575.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20575/head:pull/20575

PR: https://git.openjdk.org/jdk/pull/20575