Cannot configure switch if there is a wire in the project

[Marco Giusti]

Steps to reproduce the bug:

1. create a switch
2. create a wire
3. try to configure the switch

Here the problematic code, invoked when the "Show settings" button is pressed:

 if t == "Switch" and key == 'numports':
  nports = 0
  for it in iter(self.brickfactory.bricks):
   for p in it.plugs:
    if p.sock.nickname == b.socks[0].nickname:
     nports += 1

The wires plugs are not configured and the sock attribute is None. Here the traceback:

2013-05-23 08:53:16,956 [ERROR] [MainThread] virtualbricks.brickfactory:691 'NoneType' object has no attribute 'nickname'
Traceback (most recent call last):
  File "/home/marco/.virtualenvs/virtualbricks/src/vb-debug/virtualbricks/gui/gui.py", line 2202, in on_button_togglesettings_clicked
    self.curtain_up()
  File "/home/marco/.virtualenvs/virtualbricks/src/vb-debug/virtualbricks/gui/gui.py", line 1283, in curtain_up
    self._curtain_up()
  File "/home/marco/.virtualenvs/virtualbricks/src/vb-debug/virtualbricks/gui/gui.py", line 1321, in _curtain_up
    config_prepare()
  File "/home/marco/.virtualenvs/virtualbricks/src/vb-debug/virtualbricks/gui/gui.py", line 931, in config_brick_prepare
    if p.sock.nickname == b.socks[0].nickname:
AttributeError: 'NoneType' object has no attribute 'nickname'