Comments placed directly under page seperator in md files causes error

[falconmick]

Describe the bug

If you start the slide with a comment it will crash out with the following:

[Vue warn]: Unhandled error during execution of component update 
  at <AsyncComponentWrapper> 
  at <SlideWrapper key="40" clicks-context= 
Object { current: Getter & Setter, clicksStart: 0, relativeSizeMap: Getter, maxMap: Getter, isMounted: Getter, setup: setup(), calculateSince: calculateSince(rawAt, size), calculateRange: calculateRange(rawAt), calculate: calculate(at), register: register(el, info)
, … }
 route= 
Object { no: 4, meta: Proxy, load: async load4()
, component: {…} }
  ... > 
  at <TransitionGroup id="slideshow" tag="div" class=""  ... > 
  at <SlidesShow render-context="slide" > 
  at <SlideContainer style= 
Object { background: "var(--slidev-slide-container-background, black)" }
 is-main="" onPointerdown=fn<onClick>  ... > 
  at <Play onVnodeUnmounted=fn<onVnodeUnmounted> ref=Ref< 
Proxy { <target>: Proxy, <handler>: {…} }
 > > 
  at <RouterView> 
  at <App> [runtime-core.esm-bundler.js:51:12](https://rlmibmplyqgithub-lhp1--3030--d20a0a75.local-corp.webcontainer.io/node_modules/.pnpm/@vue+runtime-core@3.5.13/node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js?v=d9ecd089)
Uncaught (in promise) DOMException: String contains an invalid character
    patchAttr runtime-dom.esm-bundler.js:620
    patchProp runtime-dom.esm-bundler.js:793
    mountElement runtime-core.esm-bundler.js:4873
    processElement runtime-core.esm-bundler.js:4820

My guess is the unplugin-vue-markdown library being used is making an empty component and causing a blow up inside of SlidesShow. Tonight has been the very first night I have ever used vue and my tooling isn't really setup to dig any further. I hope this helps.

The bug I would classify as somewhat important as if I wasn't so stubborn I would have 100% abandoned sli.dev and moved on as this broke my slideshow completely and was making it unusable. It took me so long to notice because I wrote the entire presentations words prior to the slides inside of my md file.

Minimal reproduction

---
<--
Wow Much Commpent
-->

---

Reproduction in stackblitz

NOTE: if there is a blank line between --- and <!-- the error goes away
NOTE: if you have no more slides on left and place a <!-- comment block the error does not happen

Environment

• Slidev version: 51.0.2
• Browser: Chrome/Firefox (appears logic not browser issue)
• OS: Windows