On some com.apple.dock.plist files, there is no `len()` when looking at `self.items[section]`

[aysiu]

Results in this kind of error when trying to remove items:

Traceback (most recent call last):
  File "NAMEOFSCRIPT.py", line 14, in <module>
    dock.removeDockEntry(item_to_remove)
  File "/Library/Python/2.7/site-packages/docklib.py", line 130, in removeDockEntry
    found_index = self.findExistingLabel(label, section=sect)
  File "/Library/Python/2.7/site-packages/docklib.py", line 117, in findExistingLabel
    for index in range(len(self.items[section])):
TypeError: object of type 'NoneType' has no len()

[homebysix]

Resolved by #25, released in v1.0.5.