Changed a hardcoded return value into a variable because they would be the same.

umbra/words.py

@@ -249,7 +249,7 @@ class Sentence(list):
                 if self[index].has_source():
                     return index
                 index -= 1
-        return -1
+        return index
     
     def __str__(self):
         return ' '.join([word.word for word in self])