remove potential UndefinedError

transformers/modeling_xlm.py

@@ -81,8 +81,8 @@ def get_masks(slen, lengths, causal, padding_mask=None):
         mask = alen < lengths[:, None]
 
     # attention mask is the same as mask, or triangular inferior attention (causal)
-    if causal:
     bs = lengths.size(0)
+    if causal:
         attn_mask = alen[None, None, :].repeat(bs, slen, 1) <= alen[None, :, None]
     else:
         attn_mask = mask