Make endMax optional

Make endMax optional, which leaves us with beginMax, endMin & endMax as
optionals, & the following behaviour:

+--------------------------------------------------------+
| beginMin | beginMax | endMin | endMax | Result:        |
+----------+----------+--------+--------+----------------+
|    10    |          |        |        | 10/11 -> 10/11 |
+----------+----------+--------+--------+----------------+
|    10    |    15    |        |        | 10/15 -> 10/15 |
+----------+----------+--------+--------+----------------+
|    10    |    15    |   24   |        | 10/15 -> 24/25 |
+----------+----------+--------+--------+----------------+
|    10    |          |   24   |        | 10/11 -> 24/25 |
+----------+----------+--------+--------+----------------+
|    10    |    15    |        |   42   | 10/15 -> 41/42 |
+----------+----------+--------+--------+----------------+
|    10    |          |   24   |   42   | 10/11 -> 24/42 |
+----------+----------+--------+--------+----------------+
|    10    |          |        |   42   | 10/11 -> 41/42 |
+----------+----------+--------+--------+----------------+
|    10    |    15    |   24   |   42   | 10/15 -> 24/42 |
+----------+----------+--------+--------+----------------+

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>