pgsql: Fix unportable use of isprint().

Fix unportable use of isprint().

We must cast the arguments of <ctype.h> functions to unsigned
char to avoid problems where char is signed.

Speaking of which, considering that this *is* a <ctype.h> function,
it's rather remarkable that we aren't seeing more complaints about
not having included that header.

Per buildfarm.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9e20406dd847d0f8c1cbd803786c6d0ad33bcbdd

Modified Files
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src/interfaces/libpq/fe-trace.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)