Replace dummy input index for dict feature field from 2 to 1 since 2 …

…might not exist for data with no dictionary features (facebookresearch#438)

Summary:
Pull Request resolved: facebookresearch#438

Motivation: model trained without dictionary feature failed to export f106767664.

Reviewed By: seayoung1112

Differential Revision: D14734267

fbshipit-source-id: 28e6eff71155c9cdd8b8c0040c382b053fb5546f

pytext/fields/dict_field.py

@@ -13,7 +13,7 @@
 
 class DictFeatureField(VocabUsingField):
     dummy_model_input = (
-        torch.tensor([[2], [2]], dtype=torch.long, device="cpu"),
+        torch.tensor([[1], [1]], dtype=torch.long, device="cpu"),
         torch.tensor([[1.5], [2.5]], dtype=torch.float, device="cpu"),
         torch.tensor([1, 1], dtype=torch.long, device="cpu"),
     )