fix: validate chunk type before processing to prevent AttributeError (#9698)

### What problem does this PR solve?

This PR fixes a critical bug in the session listing endpoint where the
application crashes with an `AttributeError` when processing chunk data
that contains non-dictionary objects.

**Error before fix:**
```json
{
  "code": 100,
  "data": null,
  "message": "AttributeError(\"'str' object has no attribute 'get'\")"
}
```

**Root cause:**
The code assumes all items in the `chunks` array are dictionary objects
and directly calls the `.get()` method on them. However, in some cases,
the chunks array contains string objects or other non-dictionary types,
causing the application to crash when attempting to call `.get()` on a
string.

**Solution:**
Added type validation to ensure each chunk is a dictionary before
processing. Non-dictionary chunks are safely skipped, preventing the
crash while maintaining functionality for valid chunk data.

This fix improves the robustness of the session listing endpoint and
ensures users can retrieve their conversation sessions without
encountering server errors due to data format inconsistencies.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/sdk/session.py

@@ -562,6 +562,9 @@ def list_agent_session(tenant_id, agent_id):
                             "chunks" in conv["reference"][chunk_num]):
                         chunks = conv["reference"][chunk_num]["chunks"]
                         for chunk in chunks:
+                            # Ensure chunk is a dictionary before calling get method
+                            if not isinstance(chunk, dict):
+                                continue
                             new_chunk = {
                                 "id": chunk.get("chunk_id", chunk.get("id")),
                                 "content": chunk.get("content_with_weight", chunk.get("content")),