Mathex Editor 'Clear Set' does nothing and other bugs

[QinCai-rui]

By the looks of it, the question editor's "Clear Set" does nothing.

Also, questions and answers could be null which may make the players be confused; adding a json file validator code might help. See below:

Also, when the question requires a number but the player enters a string or others, a pop up will say 'answer is null' as well, which is also quite confusing.

[QinCai-rui]

maths/src/routes/(mathex)/mathex/app/create/editor/+page.svelte

Line 104 in a48a602

<Menubar.Item>Clear Set</Menubar.Item>