Fixed #364

[thakyZ]

The cause of this issue was because of these steps.

1. The list couldn't be dragged downward thus returning null to ModToIdConverter
2. The list was unable to insert the value at an index that was changed.
3. The length of the index when dragging becomes 1 if the list is 2
4. Since the length was 1 it would try to insert the value at index 1 (length of 2)

This has been tested by me, someone should try it as well.

[thakyZ]

I had fixed the issue somewhat in d651ea1 but when I did some more testing the issue sort of still persisted if you were going to try to bug it out, which wasn't hard to do, so I made commit 7f37aca to try to fix that, and it seems to work.