Path + String produces bad AnySequence result if Path ends with / and String starts with /

[Lily Ballard]

When adding a String to a Path, if the Path ends with / and the String starts with / then the results include AnySequence garbage.

import FileKit

print(Path("/Foo/bar/") + "/wat")
// prints:
// /Foo/bar/AnySequence<Path>(_box: Swift._SequenceBox<Swift._DropFirstSequence<FileKit.DirectoryEnumerator>>)

Tested with the latest develop (7521741) on Swift 4.1.2.