fix: handle undefined ip_hidden_states in self-attention path

[Mr-Neutr0n]

Summary

• In IPAttnProcessor.forward() and IPAttnProcessor2_0.forward(), the variable ip_hidden_states is only assigned in the else branch (cross-attention path), but is referenced unconditionally in the ip-adapter computation block that follows. When encoder_hidden_states is None (self-attention), this causes a NameError.
• This fix initializes ip_hidden_states = None in the self-attention branch and guards the ip-adapter computation with if ip_hidden_states is not None:, so the processor gracefully skips ip-adapter blending during self-attention.

Test plan

• Verify that the processor no longer raises NameError when encoder_hidden_states is None
• Verify that cross-attention with ip-adapter embeddings still works as before
• Verify region control behavior is unchanged when ip_hidden_states is present