Calling toChar(0 / 0) causes e2 to crash.

[nick100lay]

Describe the bug
Bug in lua/entities/gmod_wire_expression2/core/string.lua 122: e2function string toChar(number n).

Calling this with the NaN value causes a lua error, and e2 crashes.

To Reproduce
Steps to reproduce the behavior:

1. Type the code toChar(0 / 0) in the e2 editor.
2. Put the chip.
3. It will show an error hint and crash.

Expected behavior
Possible fix:

e2function string toChar(number n)
	if n ~= n or n < 0 or n > 255 then -- Check on NaN and the byte range.
		return self:throw("Invalid argument (" .. n .. ") (must be between 0 and 255)", "")
	end
	return string_char(n)
end

Also, the check above should be added in 139: e2function string toUnicodeChar(number byte) and, maybe, in other places.