Fix CharacterIterator re-reading the last part of a file

src/main/java/io/github/lonamiwebs/overgram/utils/CharacterIterator.java

@@ -31,7 +31,7 @@ public class CharacterIterator implements Iterator<Character>, Iterable<Characte
             readNext();
             index = 0;
         }
-        return length != -1;
+        return index < length;
     }
 
     @Override