Revert "Removing old check of ip_adapter scale"

This reverts commit a87895e.

Author: guiyrt

src/diffusers/models/attention_processor.py

@@ -5144,7 +5144,7 @@ def __call__(
                 encoder_hidden_states = attn.to_add_out(encoder_hidden_states)
 
         # IP Adapter
-        if ip_hidden_states is not None:
+        if self.scale != 0 and ip_hidden_states is not None:
             # Norm image features
             norm_ip_hidden_states = self.norm_ip(ip_hidden_states, temb=temb)