yuzu_cmd: skip kernel teardown when nothing was booted

SDL_AppQuit runs on every exit path, including the ones where SDL_AppInit
returned early: no ROM given, --help, or --version. The kernel only exists
once a title is loaded, so Pause() and ShutdownMainProcess() walk into an
uninitialized KernelCore and the process dies with SIGSEGV. The crash lands
before spdlog flushes, which is why --version printed nothing instead of a
version line.

Guard the teardown on System::IsPoweredOn(), and ignore the null appstate
SDL passes when SDL_AppInit never stored one.

Assisted-by: Claude (Anthropic) (diagnosed the crash and wrote the guard)

0 files changed, 0 insertions, 0 deletions