pyinvoke/invoke — pull request #142 by singingwolfboy (2014-06-12 19:22:00+00:00)
Title: Check for a file descriptor before trying to close it

This was causing a traceback for me:
```traceback
% inv --list
Traceback (most recent call last):
File "/usr/local/bin/inv", line 9, in
load_entry_point('invoke==0.8.1', 'console_scripts', 'inv')()
File "/usr/local/lib/python2.7/site-packages/invoke/cli.py", line 279, in main
dispatch(sys.argv)
File "/usr/local/lib/python2.7/site-packages/invoke/cli.py", line 265, in dispatch
args, collection, parser_contexts = parse(argv, version=version)
File "/usr/local/lib/python2.7/site-packages/invoke/cli.py", line 188, in parse
collection = loader.load(start) if start else loader.load()
File "/usr/local/lib/python2.7/site-packages/invoke/loader.py", line 52, in load
fd.close()
AttributeError: 'NoneType' object has no attribute 'close'
```