pgsql: libpq: Fix PQtrace() format for non-printable characters

libpq: Fix PQtrace() format for non-printable characters

PQtrace() was generating its output for non-printable characters without
casting the characters printed with unsigned char, leading to some extra
"\xffffff" generated in the output due to the fact that char may be
signed.

Oversights introduced by commit 198b3716dba6, so backpatch down to v14.

Author: Ran Benita <ran@unusedvar.com>
Discussion: /messages/by-id/a3383211-4539-459b-9d51-95c736ef08e0@app.fastmail.com
Backpatch-through: 14

Branch
------
REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ae53537e218a112676483e50358718d142bcfeb9

Modified Files
--------------
src/interfaces/libpq/fe-trace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)