set tqdm total to None in fetch gunzip (#6377)

fixed bar overflow

python examples/beautiful_mnist.py
https://storage.googleapis.com/cvdf-datasets/mnist/train-images-idx3-ubyte.gz: 47.0MB [00:00, 136MB/s]]
https://storage.googleapis.com/cvdf-datasets/mnist/train-labels-idx1-ubyte.gz: 60.0kB [00:00, 8.66MB/s]
https://storage.googleapis.com/cvdf-datasets/mnist/t10k-images-idx3-ubyte.gz: 7.84MB [00:00, 97.5MB/s]
https://storage.googleapis.com/cvdf-datasets/mnist/t10k-labels-idx1-ubyte.gz: 10.0kB [00:00, 8.90MB/s]

tinygrad/helpers.py

@@ -272,15 +272,15 @@ def fetch(url:str, name:Optional[Union[pathlib.Path, str]]=None, subdir:Optional
   if not fp.is_file() or not allow_caching:
     with urllib.request.urlopen(url, timeout=10) as r:
       assert r.status == 200
-      total_length = int(r.headers.get('content-length', 0))
-      progress_bar = tqdm(total=total_length, unit='B', unit_scale=True, desc=f"{url}", disable=CI)
+      length = int(r.headers.get('content-length', 0)) if not gunzip else None
+      progress_bar = tqdm(total=length, unit='B', unit_scale=True, desc=f"{url}", disable=CI)
       (path := fp.parent).mkdir(parents=True, exist_ok=True)
       readfile = gzip.GzipFile(fileobj=r) if gunzip else r
       with tempfile.NamedTemporaryFile(dir=path, delete=False) as f:
         while chunk := readfile.read(16384): progress_bar.update(f.write(chunk))
         f.close()
         progress_bar.update(close=True)
-        if (file_size:=os.stat(f.name).st_size) < total_length: raise RuntimeError(f"fetch size incomplete, {file_size} < {total_length}")
+        if length and (file_size:=os.stat(f.name).st_size) < length: raise RuntimeError(f"fetch size incomplete, {file_size} < {length}")
         pathlib.Path(f.name).rename(fp)
   return fp