Certain PDF's cause errors

```
Importing 'Transformers_ch1-6forTR_8.23.24.pdf'...
Thinking...
An error occurred (ValidationException) when calling the Converse operation:
The model returned the following errors: 'utf-8' codec can't encode
character '\ud835' in position 87999: surrogates not allowed
Error: An error occurred (ValidationException) when calling the Converse
operation: The model returned the following errors: 'utf-8' codec can't
encode character '\ud835' in position 87999: surrogates not allowed
Traceback (most recent call last):
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/queueing.py", line 536, in process_events
response = await route_utils.call_process_api(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/route_utils.py", line 321, in call_process_api
output = await app.get_blocks().process_api(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/blocks.py", line 1935, in process_api
result = await self.call_function(
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/blocks.py", line 1532, in call_function
prediction = await utils.async_iteration(iterator)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/utils.py", line 671, in async_iteration
return await iterator.__anext__()
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/utils.py", line 776, in asyncgen_wrapper
response = await iterator.__anext__()
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/chat_interface.py", line 653, in _stream_fn
first_response = await async_iteration(generator)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/utils.py", line 671, in async_iteration
return await iterator.__anext__()
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/utils.py", line 664, in __anext__
return await anyio.to_thread.run_sync(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/anyio/to_thread.py", line 56, in run_sync
return await get_async_backend().run_sync_in_worker_thread(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 2177, in run_sync_in_worker_thread
return await future
^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 859, in run
result = context.run(func, *args)
^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/miniconda3/lib/python3.12/site-packages/gradio/utils.py", line 647, in run_sync_iterator_async
return next(iterator)
^^^^^^^^^^^^^^
File "/Users/admin/dev/multimodal-chat/multimodal_chat.py", line 2362, in chat_function
response = manage_conversation_flow(messages, system_prompt, temperature, state)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/admin/dev/multimodal-chat/multimodal_chat.py", line 2293, in manage_conversation_flow
response_message = response['output']['message']
~~~~~~~~^^^^^^^^^^
TypeError: string indices must be integers, not 'str'
```

Reproduce the failure by importing Transformers_ch1-6forTR_8.23.24.pdf. Start in multimodal_chat.py at chat_function around line 2362 and manage_conversation_flow around line 2293, then trace the Converse response handling. Done means this PDF no longer produces the UTF-8 ValidationException followed by the TypeError.

Written by the indexing model from the issue text.