pgsql: Use snprintf not sprintf in pg_waldump's timestamptz_to_str.

Use snprintf not sprintf in pg_waldump's timestamptz_to_str.

This could only cause an issue if strftime returned a ridiculously
long timezone name, which seems unlikely; and it wouldn't qualify
as a security problem even then, since pg_waldump (nee pg_xlogdump)
is a debug tool not part of the server. But gcc 8 has started issuing
warnings about it, so let's use snprintf and be safe.

Backpatch to 9.3 where this code was added.

Discussion: /messages/by-id/21789.1529170195@sss.pgh.pa.us

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/18933261589c9547d5c517cdc05f25362cce412a

Modified Files
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src/bin/pg_waldump/compat.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)