Fix deeplinks no matter previous scroll position

runtime/src/app/app.ts

@@ -200,7 +200,7 @@ export async function navigate(target: Target, id: number, noscroll?: boolean, h
 			if (deep_linked) {
 				scroll = {
 					x: 0,
-					y: deep_linked.getBoundingClientRect().top
+					y: deep_linked.getBoundingClientRect().top + scrollY
 				};
 			}
 		}

test/apps/scroll/src/routes/a-third-tall-page.svelte

@@ -0,0 +1,5 @@
+<h1>A third tall page</h1>
+
+<a href="tall-page#foo" id="top">link</a>
+<div style="height: 9999px"></div>
+<a href="tall-page#foo" id="bottom">link</a>

test/apps/scroll/test.ts

@@ -81,6 +81,26 @@ describe('scroll', function() {
 		assert.ok(scrollY > 0);
 	});
 
+	it('scrolls to a deeplink on a new page no matter the previous scroll position', async () => {
+		await r.load('/a-third-tall-page#top');
+		await r.sapper.start();
+		await r.sapper.prefetchRoutes();
+
+		await r.page.click('a#top');
+		await r.wait();
+		const firstScrollY = await r.page.evaluate(() => window.scrollY);
+
+		await r.load('/a-third-tall-page#bottom');
+		await r.sapper.start();
+		await r.sapper.prefetchRoutes();
+
+		await r.page.click('a#bottom');
+		await r.wait();
+		const secondScrollY = await r.page.evaluate(() => window.scrollY);
+
+		assert.equal(firstScrollY, secondScrollY);
+	});
+
 	it('survives the tests with no server errors', () => {
 		assert.deepEqual(r.errors, []);
 	});