Eliminate force-unwrap operations #9
Description
While the code is technically null-safe, there are a number of force-unwrap operations that could result in a crash. For example, the init sequence in vm.dart tries to determine the system's Culture, which may end up in a null return (and thus should use a sane default), but will just try to do culture!.id and then die. These cases should all be looked at individually and be fixed.