Logic error in TRange::Difference causes crash when you Trim and Preserve Left/Right and unbounded Attach section in the sequencer

TRange::Difference function does not handle bounds correctly, causes crash in the sequencer when "Trim And Preserve Left/Right" is used in the user's example project.
User provided a potential fix: https://github.com/EpicGames/UnrealEngine/pull/12190

1. See setup in attached repro project (Test_Seq in map Test), or create your own level sequence and add two actors, create an attach track for one of the actors to the other, and make the track unbounded.
2. Put the sequencer head in the middle of the CubeChild attach track, right click the track, and select Trim and Preserve Left or Right. Assert fails in TRange.