FPackageName::SearchForPackageOnDisk fails to find maps when using IOStore

This bug was discovered by a user who tried changing level through the 'servertravel' console command (HandleServerTravelCommand). 

Debugging shows that FindFilesAtPathInIndex won't return anything for the /Game (ie Project/Content) path. Seems like the files under IOStore are not searchable. 

• Create a test project
• Create 2 test levels (LevelA and LevelB). Make sure to save them.
• In LevelA, add some code (actor, BP node...) that will make that call: 
  • FPackageName::SearchForPackageOnDisk(TEXT("LevelB"))
• The call to SearchForPackageOnDisk will be successful in PIE. 
• Make sure that both levels are part of the cook.
• Package with IOStore, the Search will fail
• Package without IOStore, the Search will be successful