pgsql: Ensure that snprintf.c's fmtint() doesn't overflow whenprinting

Ensure that snprintf.c's fmtint() doesn't overflow when printing INT64_MIN.

This isn't actually a live bug, as the output happens to be the
same.  But it upsets tools like UBSan, which makes it worthwhile to
fix.

As it's an issue without practical consequences, don't backpatch.

Author: Andres Freund
Discussion: https://postgr.es/m/20180928001121.hhx5n6dsygqxr5wu@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4868e4468590bc32f9c3afed4ec795d6a7732c9d

Modified Files
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src/port/snprintf.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)