FPackageName::IsValidLongPackageName would fail for the root paths as the mount path roots all end with a trailing slash, however FPackageName::IsValidLongPackageName doesn't accept paths that end in a trailing slash (as it's expected to be working with names, not paths).
This change updates FAssetDataGatherer::PrioritizeSearchPath to use FPackageName::TryConvertLongPackageNameToFilename instead (which will gracefully fail on an invalid path), and SPathView makes sure that it appends a trailing slash to the path it gives to FAssetDataGatherer::PrioritizeSearchPath.
[CL 2642169 by Jamie Dale in Main branch]
466912cfbe