Handle another source of emulator errors

The unhandledrejection event handler from 89cb333
is not triggered when it exists with a non-0 status code (after successfully
booting, e.g. when trying to run MacWrite 1.0 on a too-modern OS).

src/emulator/emulator-worker.ts

@@ -562,6 +562,19 @@ function startEmulator(config: EmulatorWorkerConfig) {
         },
 
         printErr: console.warn.bind(console),
+
+        quit(status: number, toThrow?: Error) {
+            console.log("Emulator quit with status", status);
+            if (status !== 0) {
+                console.error(toThrow);
+                postMessage({
+                    type: "emulator_did_have_error",
+                    error: toThrow
+                        ? toThrow.toString()
+                        : `Exit status ${status}`,
+                });
+            }
+        },
     };
     (self as any).Module = moduleOverrides;
 

src/react-app-env.d.ts

@@ -94,3 +94,7 @@ declare module "ringbuf.js" {
         available_write(): number;
     }
 }
+
+interface EmscriptenModule {
+    quit: (status: number, toThrow?: Error) => void;
+}