pgsql: Add checks for valid multibyte character length in UtfToLocal, L

Add checks for valid multibyte character length in UtfToLocal, LocalToUtf.

This is mainly to suppress "uninitialized variable" warnings from very
recent versions of gcc.  But it seems like a good robustness thing anyway,
not to mention that we might someday decide to support 6-byte UTF8.

Per report from Karol Trzcionka.  No back-patch since there's no reason
at the moment to think this is more than cosmetic.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d9f37e6661ec654f7252bfc23e084c9e2ca5db14

Modified Files
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src/backend/utils/mb/conv.c |   15 +++++++++++++++
1 file changed, 15 insertions(+)