[macOS] Fix a TypeError in DarwinIntegration._get_favorite_list()

tTraceback (most recent call last):
  File "nxdrive/__main__.py", line 118, in main
  File "nxdrive/commandline.py", line 528, in handle
  File "nxdrive/commandline.py", line 663, in bind_server
  File "nxdrive/manager.py", line 644, in bind_server
  File "nxdrive/manager.py", line 738, in bind_engine
  File "nxdrive/manager.py", line 728, in bind_engine
  File "nxdrive/engine/engine.py", line 162, in __init__
  File "nxdrive/engine/engine.py", line 1021, in bind
  File "nxdrive/engine/engine.py", line 1065, in _check_root
  File "nxdrive/utils.py", line 625, in wrapper
  File "nxdrive/osi/darwin/darwin.py", line 304, in register_folder_link
  File "nxdrive/osi/darwin/darwin.py", line 339, in _get_favorite_list
TypeError: 'LSSharedFileListRef' object is not iterable