Fix ObjectRef crashes due to lua_isnil()

[Zughy]

So, according to Lua, when a value is not specified is not nil, but no value. And they're not the same. This should fix it

To do

This PR is Ready for Review.

How to test

Spawn an armorball and it shouldn't crash anymore

[sfan5]

I'd been meaning to ask this on the cleanup PR but it got merged before I got around. Oh well.

[sfan5]

Looks good.

[rubenwardy]

Shouldn't all of the checks be isnoneornil?

[Zughy]

Shouldn't all of the checks be isnoneornil?

Idk, for some functions is kind of silly to declare them like function(something, nil, nil nil), so I avoided that. But if it's a problem, I'll change it. Also, a few lua_isnone could be completely removed if readParam<float>(L, idx) supported a third parameter acting as default, like <bool> and strings do

[Desour]

Imho, none and nil shouldn't be distinguishable to modders, like it is for normal lua functions.

You could add the missing readParam functions with default values. (It might be less work to just implement the generic function using the generic no-default-value readParam.)

[rubenwardy]

Yeah, makes sense to remove the boolean and int/float specialisations with default values, and instead use:

template <typename T>
inline T readParam(lua_State *L, int index, const T &default_value)
{
	return lua_isnoneornil(L, index) ? default_value : readParam<T>(L, index);
}

[Zughy]

Ruben suggestion addressed. Also, I've added a couple more readParam: int and v3f, I hope it's fine

[numberZero]

LGTM

[numberZero]

btw note that v2f is spelled three times on this line (others are similar):
v2f frame_range = readParam<v2f>(L, 2, v2f(1, 1));
whether that is good is style question (NB: I’m not asking to change anything, I don’t govern the style) but two of these are redundant:
auto frame_range = readParam<v2f>(L, 2, {1, 1}); and
auto frame_range = readParam(L, 2, v2f(1, 1)); are both valid