Added a check to ensure we didn't go out of bounds of an array

The fix @evilhero  checked in yesterday (df322cc1d65422b159893e407ccb570fb36d4d0e) caused my force scan to stop working.  with the following error:

```python
Exception in thread Thread-13:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 551, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 504, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/srv/tjiddy/mylar/mylar/updater.py", line 365, in forceRescan
    if 'au' in fcnew[som+1].lower():
IndexError: list index out of range
```
I just added a check to make sure we weren't going out of bounds on the  fcnew array