Run the reference emulator silently when WebKit reports no audio sample rate

After a page process has opened many AudioContexts, WebKit can hand out
one whose sampleRate is 0. The adapter passed that rate to binjgb, whose
emulator_run_until divides by the audio frequency on every call, so the
first frame trapped with "Division by zero". This failed the Day-Care
cartridge comparisons on WebKit after earlier tests had created hundreds
of emulators, and could crash the reference player in Safari.

A context without a usable rate is now closed and the emulator runs
silently at the fallback rate, as when no AudioContext can be created.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/emulator/binjgb.ts

@@ -59,11 +59,17 @@ export class BinjgbEmulator implements Emulator {
       // Audio is optional. Failure must not block a silent game.
       try {
         this.audio = new AudioContext();
+        // WebKit can return a context whose sample rate is 0 (seen after a
+        // page process has opened many); binjgb divides by the rate.
+        if (!(this.audio.sampleRate > 0))
+          throw new Error("No audio sample rate.");
         this.gain = this.audio.createGain();
         this.gain.gain.value = this.muted ? 0 : 0.4;
         this.gain.connect(this.audio.destination);
       } catch {
+        void this.audio?.close().catch(() => {});
         this.audio = undefined;
+        this.gain = undefined;
       }
       this.romPointer = this.module._malloc(rom.length);
       if (!this.romPointer) throw new Error("Could not allocate ROM memory.");