Using variable 'task' before assignment

When running the demo UI with agents created via https://mozilla-ai.github.io/any-agent/serving/#__tabbed_1_2, I ran into the following exception.

https://github.com/google-a2a/a2a-samples/blob/08dde55c070f43be3fc2abf9ff976b689891991f/samples/python/hosts/multiagent/host_agent.py#L179

```
xception in thread Thread-1 ():
Traceback (most recent call last):
File "/Users/nbrake/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/threading.py", line 1075, in _bootstrap_inner
self.run()
File "/Users/nbrake/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/threading.py", line 1012, in run
self._target(*self._args, **self._kwargs)
File "/Users/nbrake/scm/a2a-samples/demo/ui/service/server/server.py", line 98, in
target=lambda: asyncio.run(self.manager.process_message(message))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/nbrake/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/asyncio/runners.py", line 194, in run
return runner.run(main)
^^^^^^^^^^^^^^^^
File "/Users/nbrake/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/nbrake/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/asyncio/base_events.py", line 686, in run_until_complete
return future.result()
^^^^^^^^^^^^^^^
File "/Users/nbrake/scm/a2a-samples/demo/ui/service/server/adk_host_manager.py", line 186, in process_message
async for event in self._host_runner.run_async(
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/runners.py", line 196, in run_async
async for event in invocation_context.agent.run_async(invocation_context):
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/agents/base_agent.py", line 147, in run_async
async for event in self._run_async_impl(ctx):
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/agents/llm_agent.py", line 278, in _run_async_impl
async for event in self._llm_flow.run_async(ctx):
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 279, in run_async
async for event in self._run_one_step_async(invocation_context):
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 309, in _run_one_step_async
async for event in self._postprocess_async(
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 381, in _postprocess_async
async for event in self._postprocess_handle_function_calls_async(
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 456, in _postprocess_handle_function_calls_async
if function_response_event := await functions.handle_function_calls_async(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/functions.py", line 166, in handle_function_calls_async
function_response = await __call_tool_async(
^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/functions.py", line 431, in __call_tool_async
return await tool.run_async(args=args, tool_context=tool_context)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/nbrake/scm/a2a-samples/demo/ui/.venv/lib/python3.12/site-packages/google/adk/tools/function_tool.py", line 80, in run_async
return await self.func(**args_to_call) or {}
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/nbrake/scm/a2a-samples/samples/python/hosts/multiagent/host_agent.py", line 179, in send_message
return await convert_parts(task.parts, tool_context)
^^^^
UnboundLocalError: cannot access local variable 'task' where it is not associated with a value
```