"AttributeError: 'NoneType' object has no attribute 'decode'" when executing empty script

还没有人认领这个 Issue。

Wouldn't it be natural that executing a script with only comments is a no-op returning OK?
Such that for example commenting out the contents of a migration script while developing runs the script as a no-op.

Instead what happens when running this:
```
import os
import asyncpg
import asyncio

async def main():
conn = await asyncpg.connect(os.environ["DATABASE_URI"])
async with conn.transaction():
await conn.execute("-- hello")

if __name__ == "__main__":
asyncio.run(main())
```

Is this:
```
Traceback (most recent call last):
File "/home/msa/dev/sandbox/pgtesting/hello.py", line 13, in
asyncio.run(main())
~~~~~~~~~~~^^^^^^^^
File "/home/msa/.local/share/uv/python/cpython-3.13.0-linux-x86_64-gnu/lib/python3.13/asyncio/runners.py", line 194, in run
return runner.run(main)
~~~~~~~~~~^^^^^^
File "/home/msa/.local/share/uv/python/cpython-3.13.0-linux-x86_64-gnu/lib/python3.13/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/home/msa/.local/share/uv/python/cpython-3.13.0-linux-x86_64-gnu/lib/python3.13/asyncio/base_events.py", line 721, in run_until_complete
return future.result()
~~~~~~~~~~~~~^^
File "/home/msa/dev/sandbox/pgtesting/hello.py", line 9, in main
await conn.execute("-- hello")
File "/home/msa/dev/sandbox/pgtesting/.venv/lib/python3.13/site-packages/asyncpg/connection.py", line 349, in execute
result = await self._protocol.query(query, timeout)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "asyncpg/protocol/protocol.pyx", line 375, in query
File "asyncpg/protocol/protocol.pyx", line 888, in asyncpg.protocol.protocol.BaseProtocol._dispatch_result
File "asyncpg/protocol/protocol.pyx", line 815, in asyncpg.protocol.protocol.BaseProtocol._on_result__simple_query
AttributeError: 'NoneType' object has no attribute 'decode'
```
Setup is just
```
mkdir hello
cd hello
uv init .
uv add asyncpg
export DATABUTTON_URI="something"
uv run hello.py # above example
```

从 asyncpg/connection.py 中的 Connection.execute 开始，跟踪 asyncpg/protocol/protocol.pyx 中展示的协议查询路径，尤其是 _on_result__simple_query。重现仅包含注释的查询，然后添加或更新覆盖测试，使其能够成功完成而不会出现 NoneType 解码错误，并保留非空查询的正常结果。

由索引模型根据 Issue 内容生成。