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)

1 files changed, 10 insertions, 2 deletions

diff --git a/src/yuzu_cmd/yuzu.cpp b/src/yuzu_cmd/yuzu.cpp
index 70fd9090e3..22abe6a759 100644
--- a/src/yuzu_cmd/yuzu.cpp
+++ b/src/yuzu_cmd/yuzu.cpp
@@ -491,9 +491,17 @@ extern "C" SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event) {
 }
 extern "C" void SDL_AppQuit(void *appstate, SDL_AppResult result) {
     SdlState *state = (SdlState *)appstate;
+    if (!state) {
+        return;
+    }
     state->system.DetachDebugger();
-    void(state->system.Pause());
-    state->system.ShutdownMainProcess();
+    // SDL calls this even when SDL_AppInit never powered the system on (no ROM given, --help or
+    // --version): the kernel is uninitialised then, and Pause()/ShutdownMainProcess() would
+    // dereference it.
+    if (state->system.IsPoweredOn()) {
+        void(state->system.Pause());
+        state->system.ShutdownMainProcess();
+    }
     delete state;
 }