When start date == due date, report todo length 0

Otherwise the wrong start date is calculated when advancing a recurring
todo item.

The progress color will still use a length of 1 for calculating the
appropriate color.

topydo/lib/Todo.py

@@ -94,7 +94,5 @@ class Todo(TodoBase):
         if start and due and start < due:
             diff = due - start
             return diff.days
-        elif start and due and start == due:
-            return 1
         else:
             return 0