psql: call clearerr() just before printing

We were never doing clearerr() on the output stream, which results in a
message being printed after each result once an EOF is seen:

could not print result table: Success

This message was added by commit b03436994bcc (in the pg13 era); before
that, the error indicator would never be examined.  So backpatch only
that far back, even though the actual bug (to wit: the fact that the
error indicator is never cleared) is older.

src/fe_utils/print.c

@@ -3347,6 +3347,9 @@ printTable(const printTableContent *cont,
 		is_local_pager = is_pager;
 	}
 
+	/* clear any pre-existing error indication on the output stream */
+	clearerr(fout);
+
 	/* print the stuff */
 
 	if (flog)