safer token counting in messages (#19599)

Author: logan-markewich

llama-index-core/llama_index/core/utilities/token_counting.py

@@ -66,7 +66,7 @@ def estimate_tokens_in_messages(self, messages: List[ChatMessage]) -> int:
                 tokens += 3  # Additional tokens for function call
 
             if "tool_calls" in additional_kwargs:
-                for tool_call in additional_kwargs["tool_calls"]:
+                for tool_call in additional_kwargs.get("tool_calls", []):
                     if (
                         hasattr(tool_call, "function")
                         and tool_call.function is not None