Also removing redundant defer for env.PatchAll(), which is now automatically
handled in t.Cleanup()
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
If no env-vars were loaded from "files", and "overrides" was nil,
the code returned an empty slice instead of a `nil` value.
Also add a test for this function, as no unit test was present yet.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
