fix: locale parsing related crash on some mpv builds (#794)

The # operator produces different results on luajit to the
interpreter for lists like `{1, nil, 3}`.
The interpreter gives a size of 3, while luajit says it's 1.

That caused `table_assign` and `itable_join` to behave differently depending
on the lua environment they're running in.

To get the total number of vararg arguments, `select('#', ...)`` can be
used, which doesn't stop counting when it encounters `nil`.

Any error return nil.

src/uosc/lib/intl.lua

@@ -26,18 +26,19 @@ function get_locale_from_json(path)
 
 	local meta, meta_error = utils.file_info(expand_path)
 	if not meta or not meta.is_file then
-		return {}
+		return nil
 	end
 
 	local json_file = io.open(expand_path, 'r')
 	if not json_file then
-		return {}
+		return nil
 	end
 
 	local json = json_file:read('*all')
 	json_file:close()
 
-	return utils.parse_json(json)
+	local json_table = utils.parse_json(json)
+	return json_table
 end
 
 ---@param text string

src/uosc/lib/std.lua

@@ -160,7 +160,7 @@ end
 ---@return T[]
 function itable_join(...)
 	local args, result = {...}, {}
-	for i = 1, #args do
+	for i = 1, select('#', ...) do
 		if args[i] then for _, value in ipairs(args[i]) do result[#result + 1] = value end end
 	end
 	return result
@@ -201,8 +201,8 @@ end
 ---@return T
 function table_assign(target, ...)
 	local args = {...}
-	for i = 1, #args do
-		if args[i] then for key, value in pairs(args[i]) do target[key] = value end end
+	for i = 1, select('#', ...) do
+		if type(args[i]) == 'table' then for key, value in pairs(args[i]) do target[key] = value end end
 	end
 	return target
 end