Attempting to delete subtitles in lua throws

[Didas-git]

The documentation mentions subtitles[i] = nil as a way to delete subtitles, this also happens to be the only viable way to do so from C as currently, the .delete method via closures is unusable due to it relying on the stack size instead of upvalues.

The issue seems to be caused by the check_uint in this block:

Aegisub/src/auto4_lua_assfile.cpp

Lines 511 to 519 in 1ad6844

	else {
	ids.reserve(itemcount);
	while (itemcount > 0) {
	size_t n = check_uint(L, -1);
	argcheck(L, n > 0 && n <= lines.size(), itemcount, "Out of range line index");
	ids.push_back(n - 1);
	--itemcount;
	}
	}