fix: error message XSS vulnerability

[catnose99]

There is a XSS vulnerability around error handling.
Here are some examples.

$$"<img/src=./ onerror=alert(location)>
e^{i\theta} = i\sin\thetae^{i\theta}
$$

$$
e^{i\theta"<img/src=./ onerror=alert(location)>} = \cos\theta + i\sin\thetae^{i\theta} 
$$

I made a change to escape tex string.

Thank you!

[snoopysecurity]

Hey @goessner, any chance you could review this PR and fix this XSS issue?

[goessner]

Hi @catnose99 ... thanks for fixing that critical vulnerability ... sorry for lasting so long, to be able to get active here again.

--

sg