Check for NoneType on self.items[section]

Addresses this issue:
#24

Author: aysiu

payload/Library/Python/2.7/site-packages/docklib.py

@@ -114,9 +114,10 @@ def save(self):
     def findExistingLabel(self, test_label, section="persistent-apps"):
         """Returns index of item with label matching test_label or -1 if not
         found."""
-        for index in range(len(self.items[section])):
-            if self.items[section][index]["tile-data"].get("file-label") == test_label:
-                return index
+        if self.items[section]:
+            for index in range(len(self.items[section])):
+                if self.items[section][index]["tile-data"].get("file-label") == test_label:
+                    return index
 
         return -1