Fix PageController throws when changing page before viewPortDimensions are set (#153017)

## Description

This PR fixes `PageController` throwing when using `jumpToPage` or `animateToPage` to switch page before the viewport dimensions were retrieved.

Solution based on flutter/flutter#152947 (comment).

## Related Issue

Fixes flutter/flutter#86222.
Fixes flutter/flutter#152079

## Tests

Adds 2 tests.

Author: bleroux

packages/flutter/lib/src/widgets/page_view.dart

@@ -200,6 +200,11 @@ class PageController extends ScrollController {
       return Future<void>.value();
     }
 
+    if (!position.hasViewportDimension) {
+      position._pageToUseOnStartup = page.toDouble();
+      return Future<void>.value();
+    }
+
     return position.animateTo(
       position.getPixelsFromPage(page.toDouble()),
       duration: duration,
@@ -218,6 +223,11 @@ class PageController extends ScrollController {
       return;
     }
 
+    if (!position.hasViewportDimension) {
+      position._pageToUseOnStartup = page.toDouble();
+      return;
+    }
+
     position.jumpTo(position.getPixelsFromPage(page.toDouble()));
   }
 

packages/flutter/test/widgets/page_view_test.dart

@@ -1413,4 +1413,62 @@ void main() {
     expect(find.text('null'), findsNothing);
     expect(currentPage, 'not empty');
   });
+
+  testWidgets('Does not crash when calling jumpToPage before layout', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/86222.
+    final PageController controller = PageController();
+    addTearDown(controller.dispose);
+
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: Navigator(
+          onDidRemovePage: (Page<Object?> page) {},
+          pages: <Page<void>>[
+            MaterialPage<void>(child: Scaffold(
+              body: PageView(
+                controller: controller,
+                children: const <Widget>[
+                  Scaffold(body: Text('One')),
+                  Scaffold(body: Text('Two')),
+                ],
+              ),
+            )),
+            const MaterialPage<void>(child: Scaffold()),
+          ],
+        ),
+      )
+    ));
+
+    controller.jumpToPage(1);
+    expect(tester.takeException(), null);
+  });
+
+  testWidgets('Does not crash when calling animateToPage before layout', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/86222.
+    final PageController controller = PageController();
+    addTearDown(controller.dispose);
+
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: Navigator(
+          onDidRemovePage: (Page<Object?> page) {},
+          pages: <Page<void>>[
+            MaterialPage<void>(child: Scaffold(
+              body: PageView(
+                controller: controller,
+                children: const <Widget>[
+                  Scaffold(body: Text('One')),
+                  Scaffold(body: Text('Two')),
+                ],
+              ),
+            )),
+            const MaterialPage<void>(child: Scaffold()),
+          ],
+        ),
+      )
+    ));
+
+    controller.animateToPage(1, duration: const Duration(milliseconds: 50), curve: Curves.bounceIn);
+    expect(tester.takeException(), null);
+  });
 }