pgsql: Correct a thinko in pgbench that might result in incorrectly

Log Message:
-----------
Correct a thinko in pgbench that might result in incorrectly ignoring an
error condition when executing some DDL. Per report from ITAGAKI Takahiro.

Modified Files:
--------------
pgsql/contrib/pgbench:
pgbench.c (r1.35 -> r1.36)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgbench/pgbench.c.diff?r1=1.35&r2=1.36)