Problems with logging in some systems

In some systems the function locale.getpreferredencoding() may return an empty string. It this is used as an input to "decode" it will raise an error.
The code "msg = msg.decode(locale.getpreferredencoding())" that can be found in astropy/utils/console.py raises an error when it is run within the Python console emulator of PyCharm and a Warning is issued.

````
Traceback (most recent call last):
  File "/Users/jsm/Documents/proyectos/test_AMIGA_data/test_error1.py", line 11, in <module>
    vo_table = parse(vo_table_raw)
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/io/votable/table.py", line 116, in parse
    config=config, pos=(1, 1)).parse(iterator, config)
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/io/votable/tree.py", line 3066, in parse
    vo_warn(W21, config['version'], config, pos)
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/io/votable/exceptions.py", line 115, in vo_warn
    _suppressed_warning(warning, config, stacklevel=stacklevel+1)
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/io/votable/exceptions.py", line 71, in _suppressed_warning
    warn(warning, stacklevel=stacklevel+1)
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/logger.py", line 167, in _showwarning
    self.warning(message)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 1161, in warning
    self._log(WARNING, msg, args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 1268, in _log
    self.handle(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 1278, in handle
    self.callHandlers(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 1318, in callHandlers
    hdlr.handle(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 749, in handle
    self.emit(record)
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/logger.py", line 337, in _stream_formatter
    color_print(record.levelname, 'brown', end='')
  File "/Users/jsm/test_AMIGA/lib/python2.7/site-packages/astropy/utils/console.py", line 205, in color_print
    msg = msg.decode(locale.getpreferredencoding())
LookupError: unknown encoding: 
``` 

Although this problem can be unusual, I think that it could be solved if a safe fallback encoding (probably "US-ASCII") is specified for these cases.