bricks: Fix the error message when unique_fd::open fails.

        }

        template< typename... args_t >

        static unique_fd open( args_t... args )

        static unique_fd open( const char *path, args_t... args )

        {

            int raw = ::open( args... );

            int raw = ::open( path, args... );

            if ( raw < 0 )

                raise_sys() << "error opening file" << brq::format( args... );

                raise_sys() << "error opening file " << path;

            else

                return from_raw( raw );