train_samples check fix

Author: stas00

megatron/training.py

@@ -835,11 +835,11 @@ def build_train_valid_test_data_iterators(
 
     # Backward compatibility, assume fixed batch size.
     if args.iteration > 0 and args.consumed_train_samples == 0:
-        assert args.train_samples is None, \
+        assert args.train_samples is not None, \
             'only backward compatiblity support for iteration-based training'
         args.consumed_train_samples = args.iteration * args.global_batch_size
     if args.iteration > 0 and args.consumed_valid_samples == 0:
-        assert args.train_samples is None, \
+        assert args.train_samples is not None, \
             'only backward compatiblity support for iteration-based training'
         args.consumed_valid_samples = (args.iteration // args.eval_interval) * \
             args.eval_iters * args.global_batch_size