This allows building sourcekitd and swift-refactor with `SWIFT_BUILD_SWIFT_SYNTAX=NO`. In these builds, the `relatedidents` and `find-syntactic-rename-ranges` requests will always return an error.
This was causing local refactorings (which are line+column-based) to fail due to
the provided location being considered invalid, even though the available
refactorings request (which uses offset directly) reported them as available.
