fix(memory): filter non-image file types in prompt message content

- Skip non-image files when converting file objects to prompt message content.
- Ensures only image files are processed, improving the accuracy and relevance of prompt messages.

api/core/memory/token_buffer_memory.py

@@ -1,7 +1,7 @@
 from typing import Optional
 
 from core.app.app_config.features.file_upload.manager import FileUploadConfigManager
-from core.file import file_manager
+from core.file import FileType, file_manager
 from core.model_manager import ModelInstance
 from core.model_runtime.entities import (
     AssistantPromptMessage,
@@ -98,7 +98,10 @@ class TokenBufferMemory:
                     prompt_message_contents: list[PromptMessageContent] = []
                     prompt_message_contents.append(TextPromptMessageContent(data=message.query))
                     for file_obj in file_objs:
-                        prompt_message_contents.append(file_manager.to_prompt_message_content(file_obj))
+                        if file_obj.type != FileType.IMAGE:
+                            continue
+                        prompt_message = file_manager.to_prompt_message_content(file_obj)
+                        prompt_message_contents.append(prompt_message)
 
                     prompt_messages.append(UserPromptMessage(content=prompt_message_contents))
             else: