RFR: JDK-8312612: handle WideCharToMultiByte return values

[Matthias Baesken]

The function WideCharToMultiByte is used at a number of places of the JDK codebase for conversion purposes.
Unfortunately, the function might fail because of various reasons, so the return value must be checked to avoid undefined behavior or even crashes.
see
https://learn.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-widechartomultibyte
especially
https://learn.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-widechartomultibyte#return-value

At most places in the coding the return values are already checked, but some are missing.

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Commit messages:
 - JDK-8312612

Changes: https://git.openjdk.org/jdk/pull/15015/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15015&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312612
  Stats: 33 lines in 3 files changed: 20 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/15015.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15015/head:pull/15015

PR: https://git.openjdk.org/jdk/pull/15015