use explicit check as 'not 0' was still falling through

Author: winglian

src/accelerate/utils/dataclasses.py

@@ -2999,7 +2999,7 @@ def active_mesh_dims(self):
 
     def build_device_mesh(self, device_type: str):
         mesh = self.get_mesh()
-        if not len(list(mesh)):
+        if len(list(mesh)) == 0:
             return
         mesh_dim_names, mesh_shape = mesh
         device_mesh = torch.distributed.init_device_mesh(