[2.0 / next] An unowned memo with an isPending() reader skips its recompute: reads undefined after a landing, or keeps a stale value after an error recovers #4366

let release;
const m0 = createMemo(() => new Promise(r => (release = r)));
const m1 = createMemo(() => m0() + 1);
render(() => (
  <Loading fallback="[L]">
    <Show when={m0()}><span>{String(isPending(m1))} {String(m1())}</span></Show>
  </Loading>
), el);
flush(); release(2); // after settling: <span>false NaN</span>, expected <span>false 3</span>

const [s0, set0] = createSignal(3);
const [s1, set1] = createSignal(3);
const m0 = createMemo(() => { const v = s1() + s0() + 1; if (v % 4 === 2) throw new Error("m0:" + v); return v; });
const m1 = createMemo(() => m0() + 1);
render(() => (
  <Errored fallback={e => `[E ${e()?.message}]`}>
    <Show when={latest(m0)} fallback="[F]"><span>{String(isPending(m1))} {String(m1())}</span></Show>
  </Errored>
), el);
set1(2); // [E m0:6], as expected
set0(2); // <span>false 8</span>, expected <span>false 6</span> (m0 = 5)