Bug 933192 - [Settings] can join hidden wifi network without ssid name r=ejchen

Bug 933192 - [Settings] can join hidden wifi network without ssid name r=ejchen
Like this :
```javascript
!WifiHelper.isValidInput(key, password.value, identity.value,
  ssidStr, eap.value);
```

The number of spaces was wrong before, please help to fix this, thanks :)