Fix error message shown in "validate_full_path" when not authenticated

[davecap]

Example:

import solvebio
solvebio.api_key = None
SolveClient(token=None).Object.validate_full_path("~/asdf")

Exception: Could not determine vault from "~/asdf". Full path must be in one of the following formats: "vault:/path", "domain:vault:/path", or "~/path"