touchscreen: whoops, fix up script tag (#3786)

followup to https://github.com/tldraw/tldraw/pull/3765

### Change Type

<!-- ❗ Please select a 'Scope' label ❗️ -->

- [x] `sdk` — Changes the tldraw SDK
- [ ] `dotcom` — Changes the tldraw.com web app
- [ ] `docs` — Changes to the documentation, examples, or templates.
- [ ] `vs code` — Changes to the vscode plugin
- [ ] `internal` — Does not affect user-facing stuff

<!-- ❗ Please select a 'Type' label ❗️ -->

- [x] `bugfix` — Bug fix
- [ ] `feature` — New feature
- [ ] `improvement` — Improving existing features
- [ ] `chore` — Updating dependencies, other boring stuff
- [ ] `galaxy brain` — Architectural changes
- [ ] `tests` — Changes to any test code
- [ ] `tools` — Changes to infrastructure, CI, internal scripts,
debugging tools, etc.
- [ ] `dunno` — I don't know

apps/dotcom/src/pages/public-touchscreen-side-panel.tsx

@@ -1,9 +1,15 @@
 import { useEffect } from 'react'
+import { Helmet } from 'react-helmet-async'
 import '../../styles/globals.css'
 
 export function Component() {
 	useEffect(() => {
 		async function createSession() {
+			if ('meet' in window === false) {
+				setTimeout(createSession, 100)
+				return
+			}
+
 			const session = await (window as any).meet.addon.createAddonSession({
 				cloudProjectNumber: `${process.env.GOOGLE_CLOUD_PROJECT_NUMBER}`,
 			})
@@ -20,8 +26,10 @@ export function Component() {
 
 	return (
 		<>
-			{/* eslint-disable @next/next/no-sync-scripts */}
-			<script src="https://www.gstatic.com/meetjs/addons/0.1.0/meet.addons.js"></script>
+			<Helmet>
+				{/* eslint-disable @next/next/no-sync-scripts */}
+				<script src="https://www.gstatic.com/meetjs/addons/0.1.0/meet.addons.js"></script>
+			</Helmet>
 			Starting a new session…
 		</>
 	)