Reject renderer work after audio shutdown

gumble/gumbleopenal/stream_regression_test.go

@@ -0,0 +1,16 @@
+package gumbleopenal
+
+import "testing"
+
+// Regression: audio cleanup could send a final render command after Destroy
+// had closed renderCh, panicking instead of safely discarding that work.
+func TestRenderRejectsWorkAfterShutdown(t *testing.T) {
+	s := &Stream{renderClosed: true}
+	called := false
+	if s.render(func() { called = true }) {
+		t.Fatal("closed renderer accepted work")
+	}
+	if called {
+		t.Fatal("closed renderer executed work")
+	}
+}