pgsql: Don't accept length of -1 in pg_locale.h APIs.

Don't accept length of -1 in pg_locale.h APIs.

Reverts ac30021356. Per discussion, that commit interfered with useful
tooling, and was not worth the special cases.

Suggested-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/s32n3tm2mjh247f3xkkxkdk7cf77hglbr3ia3hrsdjylajou7y@nlldpag3tjd5

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6d22c67c3bf5b50565062a35cbfc46075fb9c276

Modified Files
--------------
src/backend/utils/adt/pg_locale.c | 42 +++----
src/backend/utils/adt/pg_locale_builtin.c | 13 +--
src/backend/utils/adt/pg_locale_icu.c | 187 ++++++++++++++++++++++--------
src/backend/utils/adt/pg_locale_libc.c | 161 ++++++++++++-------------
src/common/unicode/case_test.c | 69 +++--------
src/common/unicode_case.c | 26 ++---
src/include/common/unicode_case.h | 8 +-
src/include/utils/pg_locale.h | 45 ++++---
8 files changed, 297 insertions(+), 254 deletions(-)