[BUG] Browser Hangs When Mermaid Code Is Invalid

I encountered an issue where the browser becomes unresponsive when invalid or unformatted Mermaid code is pasted inline into a diagram block. This results in the document freezing and failing to load properly.

Steps to Reproduce:

- Open or create a new document.
- Insert a Diagram block.
- Create a Mermaid sequence diagram, but accidentally paste the code as a single unformatted line (e.g., from the browser’s address bar).
- Save or reload the document.