fix: add fast path for function call (#9023)

Co-authored-by: tazjin <mail@tazj.in>

python/sglang/srt/function_call/function_call_parser.py

@@ -69,6 +69,8 @@ class FunctionCallParser:
         Returns:
             True if the text contains a tool call, False otherwise
         """
+        if not self.tools:
+            return False
         return self.detector.has_tool_call(text)
 
     def parse_non_stream(self, full_text: str) -> Tuple[str, list[ToolCallItem]]:
@@ -83,6 +85,8 @@ class FunctionCallParser:
             - The remaining text after parsing that was not consumed by the detector (can be treated as normal text)
             - A list of tool calls parsed from the text
         """
+        if not self.tools:
+            return full_text, []
         parsed_result = self.detector.detect_and_parse(full_text, self.tools)
         tool_call_list = parsed_result.calls
         if tool_call_list:
@@ -102,6 +106,8 @@ class FunctionCallParser:
             - The normal text that should be displayed to the user
             - A list of tool calls parsed from the chunk
         """
+        if not self.tools:
+            return chunk_text, []
         final_normal_text = ""
         final_calls = []