Custom serializer does not support `0` as return value

[alex-kinokon]

const date = devalue.stringify(value, {
	Numeric: (value) => value instanceof Numeric && value.toJSON(),
});

If Numeric#toJSON() returns 0, there’ll be a DevalueError: Cannot stringify arbitrary non-POJOs error.

Code:

devalue/src/stringify.js

Line 64 in 6f4eb8b

if (value) {