Markdown parsing failure involving dash (`-`) and escaped underscore (`\_`)

### Steps to reproduce

1. Input

```
-

\_
```

2. Send
3. Message that gets sent: `

_`

Another case:

```
a

a -> b

\_
```

results in a single collapsed paragraph:

```
a a -> b _
```

### Outcome

#### What did you expect?

Message should be sent as is.

#### What happened instead?

Message is corrupted.

### Operating system

Arch Linux

### Application version

Element version: 1.11.86 Crypto version: Rust SDK 0.7.2 (517d99b), Vodozemac 0.7.0

### How did you install the app?

Arch Linux repo

### Homeserver

termina.org.uk

### Will you send logs?

No

Reproduce both Markdown inputs in Element Web and compare the rendered and sent messages with the expected text. Trace the Markdown parsing path responsible for list markers, escaped underscores, and collapsed paragraphs; done means both examples are sent unchanged without corrupted HTML or formatting.

Written by the indexing model from the issue text.