[FIX] component: reset isRendered when reusing fiber

It is important to reset the isRendered flag to false to ensure
that other (subsequent) simultaneous calls to render will be
skipped, as the currentFiber is actually no yet (re-)rendered.

Closes #483

tests/component/component.test.ts

@@ -3463,6 +3463,51 @@ describe("async rendering", () => {
     expect(fixture.innerHTML).toBe("<div><span>2|5</span></div>");
   });
 
+  test("concurrent renderings scenario 12", async () => {
+    // In this scenario, we have a parent component that will be re-rendered
+    // several times simultaneously:
+    //    - once in a tick: it will create a new fiber, render it, but will have
+    //    to wait for its child (blocking) to be completed
+    //    - twice in the next tick: it will twice reuse the same fiber (as it is
+    //    rendered but not completed yet)
+    const def = makeDeferred();
+
+    class Child extends Component<any, any> {
+      static template = xml`<span><t t-esc="props.val"/></span>`;
+      willUpdateProps() {
+        return def;
+      }
+    }
+
+    class Parent extends Component<any, any> {
+      static template = xml`<div><Child val="state.val"/></div>`;
+      static components = { Child };
+      state = useState({ val: 1 });
+    }
+    Parent.prototype.__render = jest.fn(Parent.prototype.__render);
+
+    const parent = new Parent();
+    await parent.mount(fixture);
+    expect(fixture.innerHTML).toBe("<div><span>1</span></div>");
+    expect(Parent.prototype.__render).toHaveBeenCalledTimes(1);
+
+    parent.state.val = 2;
+    await nextTick();
+    expect(fixture.innerHTML).toBe("<div><span>1</span></div>");
+    expect(Parent.prototype.__render).toHaveBeenCalledTimes(2);
+
+    parent.state.val = 3;
+    parent.state.val = 4;
+    await nextTick();
+    expect(fixture.innerHTML).toBe("<div><span>1</span></div>");
+    expect(Parent.prototype.__render).toHaveBeenCalledTimes(3);
+
+    def.resolve();
+    await nextTick();
+    expect(fixture.innerHTML).toBe("<div><span>4</span></div>");
+    expect(Parent.prototype.__render).toHaveBeenCalledTimes(3);
+  });
+
   test("change state and call manually render: no unnecessary rendering", async () => {
     class Widget extends Component<any, any> {
       static template = xml`<div><t t-esc="state.val"/></div>`;