Infinite sections when upgrading past 4.19 can be non-infinite

In 4.20 movie scene sections changed how infinite sections worked, and some sections that could be infinite no longer had the capability. When converting the sections use the start and end time of the section for their range, so a section could convert to be shorter than expected.

1. Create a sequence in 4.19 that has an actor with an attach track
2. Set the attach track to be infinite
3. Open the project with a newer engine version
4. Open the level sequence from step 1

RESULT
The attach track section will no longer be infinite.

EXPECTED

The section should either still be infinite or fill the playback range