Fix issue where OpenAI can return "tool_calls":null in it's json

tool_call can be null when return from openAI assistant. changing  the order so it does not run into the null issue

Author: littlechu

lib/langchain/assistant.rb

@@ -309,7 +309,7 @@ def handle_user_or_tool_message
     end
 
     def set_state_for(response:)
-      if response.tool_calls.any?
+      if response.tool_calls&.any?
         :in_progress
       elsif response.chat_completion
         :completed

lib/langchain/assistant/llm/adapters/openai.rb

@@ -40,7 +40,7 @@ def build_chat_params(
           # @param tool_call_id [String] The tool call ID
           # @return [Messages::OpenAIMessage] The OpenAI message
           def build_message(role:, content: nil, image_url: nil, tool_calls: [], tool_call_id: nil)
-            Messages::OpenAIMessage.new(role: role, content: content, image_url: image_url, tool_calls: tool_calls, tool_call_id: tool_call_id)
+            Messages::OpenAIMessage.new(role: role, content: content, image_url: image_url, tool_calls: tool_calls || [], tool_call_id: tool_call_id)
           end
 
           # Extract the tool call information from the OpenAI tool call hash