Support attention mask in split attention.

comfy/ldm/modules/attention.py

@@ -239,6 +239,12 @@ def attention_split(q, k, v, heads, mask=None):
                 else:
                     s1 = einsum('b i d, b j d -> b i j', q[:, i:end], k) * scale
 
+                if mask is not None:
+                    if len(mask.shape) == 2:
+                        s1 += mask[i:end]
+                    else:
+                        s1 += mask[:, i:end]
+
                 s2 = s1.softmax(dim=-1).to(v.dtype)
                 del s1
                 first_op_done = True