ICU-21537 Fix invalid free by long locale name

[FrankYFTang]

Only free baseName when it is neither the same as fullName nor fullNameBuffer.
If we have a very long base name (say a lot of variant) and one extension, the set extension will return buffer error and
the cause Locale to reallocate buffer for fullName, but baseName is still pointing to fullNameBase.
Then later if we free baseName in the destructor we will free the memory part of the locale itself (because
it is still pointing to fullNameBuffer) . So we need to check the free of baseName not only if it is different from fullName, but also differ from fullNameBuffer.

To test

cd icu4c/source
CXXFLAGS="-fsanitize=address" CFLAGS="-fsanitize=address" ./runConfigureICU --disable-release Linux --disable-layoutex
make clean
make -j 50 tests
cd test/intl
LD_LIBRARY_PATH=lib:stubdata:tools/ctestfw:../../lib:../../stubdata:../../tools/ctestfw:$LD_LIBRARY_PATH ./intltest collate/CollationTest/TestLongLocale

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-21537
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

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[markusicu]

lgtm tnx!