pg_dump: Simplify mkdir() error checking
pg_dump: Simplify mkdir() error checking

mkdir() can check for errors itself.  We don't need to code that
ourselves again.

kmjungersen/PostgresXL,snaga/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,postmind-net/postgres-xl,snaga/postgres-xl,snaga/postgres-xl,snaga/postgres-xl,kmjungersen/PostgresXL,postmind-net/postgres-xl,kmjungersen/PostgresXL,arcivanov/postgres-xl,snaga/postgres-xl,kmjungersen/PostgresXL,arcivanov/postgres-xl,postmind-net/postgres-xl,postmind-net/postgres-xl,kmjungersen/PostgresXL,postmind-net/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl