fix: avoid JSONDecodeError for empty line stream response

[johnny0120]

r.iter_lines() may yield empty string, which results in JSONDecodeError and terminates the stream response.

the stackstrace is as follows:

File "/root/.pyenv/versions/3.10.16/lib/python3.10/concurrent/futures/_base.py", line 451, in result
    return self.__get_result()
  File "/root/.pyenv/versions/3.10.16/lib/python3.10/concurrent/futures/_base.py", line 403, in __get_result
    raise self._exception
  File "/root/Developer/github/LightRAG/.venv/lib/python3.10/site-packages/tenacity/asyncio/__init__.py", line 114, in __call__
    result = await fn(*args, **kwargs)
  File "/root/Developer/github/LightRAG/lightrag/llm.py", line 335, in ollama_model_if_cache
    for chunk in response:
  File "/root/Developer/github/LightRAG/.venv/lib/python3.10/site-packages/ollama/_client.py", line 171, in inner
    part = json.loads(line)
  File "/root/.pyenv/versions/3.10.16/lib/python3.10/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
  File "/root/.pyenv/versions/3.10.16/lib/python3.10/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/root/.pyenv/versions/3.10.16/lib/python3.10/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

the fix: check line before json.loads, continue to next line if is empty

Client

for line in r.iter_lines():
    if not line: continue
    part = json.loads(line)

AsyncClient

async for line in r.aiter_lines():
    if not line: continue
    part = json.loads(line)