Fix if condition in squad_concat data generator.
Fix if condition in squad_concat data generator.

PiperOrigin-RevId: 194976019

tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor