When formatting integral double values as JSON, ensure that at least one
decimal place is retained.

-- Testcase --
printf("%.J\n", [
	1e100,
	1.23,
	4.00,
	1.0/3*3,
]);
-- End --

-- Args --
-R
-- End --

-- Expect stdout --
[
	1e+100,
	1.23,
	4.0,
	1.0
]
-- End --
