fix: the error when encountering pure text conversations (#5088)

Signed-off-by: shpgy-shpgy <875664365@qq.com>

components/src/dynamo/trtllm/multimodal_processor.py

@@ -139,6 +139,9 @@ class MultimodalRequestProcessor:
 
         for message in messages:
             for content in message.get("content", []):
+                if isinstance(content, str):
+                    text_parts.append(content)
+                else:
                     if content.get("type") == "text":
                         text_parts.append(content.get("text", ""))
                     elif content.get("type") == "image_url":