Feature request: Warn against invalid hex input

[seritools]

Is your feature request related to a problem? Please describe.

I forgot to switch the XOR key input field from hex to UTF8. Ideally, CyberChef would have warned if the input contains non-whitespace, non-[0123456789abcdef] inputs.

https://cyberchef.org/#recipe=XOR(%7B'option':'Hex','string':'Why%20is%20this%20allowed'%7D,'Standard',false)&input=U29tZSB0ZXN0IHN0cmluZw

Describe the solution you'd like

A warning or something would be nice to see

Additional context

Wasted like 2h in flare-on because of this 🙃